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As filed with the Securities and Exchange Commission on or about April 29, 2020

Approximate date of commencement of proposed public offering: As soon as practical after the effective date of the Registration Statement.

Title of Securities Being Registered: Shares of beneficial interest, no par value

The Securities and Exchange Commission has not approved or disapproved these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

IMPORTANT NOTE: Beginning on January 1, 2021, as permitted by regulations adopted by the Securities and Exchange Commission, paper copies of the William Blair Funds’ (the “Funds”) annual and semi-annual shareholder reports will no longer be sent by mail, unless you specifically request paper copies of the shareholder reports from the Funds or from your financial intermediary, such as a broker-dealer or bank. Instead, shareholder reports will be available on the Funds’ website (https://www.williamblairfunds.com/investor_services/prospectus_reports_forms.fs), and you will be notified by mail each time a report is posted and provided with a website link to access the report.

If you already elected to receive shareholder reports electronically, you will not be affected by this change and you need not take any action. You may elect to receive shareholder reports and other communications from the Funds electronically by notifying your financial intermediary or, if you are a direct investor, by calling 1-800-742-7272.

You may elect to receive all future shareholder reports in paper free of charge. You can inform your financial intermediary that you wish to continue receiving paper copies of your shareholder reports, or if you are a direct investor, by calling 1-800-742-7272. Your election to receive reports in paper will apply to all Funds you hold directly or through your financial intermediary, as applicable.

INVESTMENT OBJECTIVE: The William Blair Growth Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

Example: This example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund’s operating expenses remain the same. The figures reflect the expense limitation for the first year. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Portfolio Turnover: The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 39% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES: The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of domestic growth companies of all sizes that are expected to exhibit quality growth characteristics. The Fund invests primarily in equity securities issued by companies that typically have market capitalizations no smaller than the smallest capitalized company, and no larger than the largest capitalized company, included in the Russell 3000^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to companies in the Russell 3000^® Index, but that may have market capitalizations outside the range of companies included in the index.

The Russell 3000^® Index is a widely recognized, unmanaged index that measures the performance of the 3,000 largest U.S. companies. The size of companies in the Russell 3000^® Index may change with market conditions. In addition, changes to the composition of the Russell 3000^® Index can change the market capitalization range of the companies in the index. As of July 1, 2019, the Russell 3000^® Index included securities issued by companies that ranged in size between $58.4 million and $1,039.7 billion. The Russell 3000^® Growth Index, the Fund’s benchmark, measures the performance of Russell 3000^® companies with higher price-to-book ratios and higher forecasted growth values.

In choosing investments, the Adviser performs fundamental company analysis and focuses on stock selection. The Adviser evaluates the extent to which a company meets the quality growth criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be, or should have the expectation of becoming, a significant provider in the primary markets it serves, (b) the company should have some distinctive attribute relative to present or potential competitors (for example, this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should participate in an industry expected to grow rapidly due to economic factors or technological change or should grow through market share gains in its industry and (d) the company should have a strong management team.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of U.S. growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Market Risk. The value of the Fund’s investments may go up or down, sometimes rapidly or unpredictably. The value of an investment may decline due to factors affecting securities markets generally or particular industries represented in the securities markets. The value of an investment may decline due to general market conditions that are not specifically related to a particular company, such as real or perceived adverse economic conditions, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. Events such as war, acts of terrorism, social unrest, natural disasters, the spread of infectious illness or other public health threats could also significantly impact the Fund and its investments. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously. Geopolitical and other events may also disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments.

Smaller Company Risk. Stocks of smaller companies involve greater risk than those of larger, more established companies. This is because smaller companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Smaller companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of smaller companies may be more volatile and less liquid than securities of large capitalized companies.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the growth investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

Focus Risk. To the extent that the Fund focuses its investments in particular industries, asset classes or sectors of the economy, any market changes affecting companies in those industries, asset classes or sectors may impact the Fund’s performance.

Operational and Technology Risk. Cyber-attacks, disruptions, or failures that affect the Fund’s service providers, counterparties, market participants, or issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of broad measures of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

full calendar year of performance history is available. After-tax returns for Class I shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). David C. Fording, a Partner of the Adviser, manages the Fund. Mr. Fording has managed or co-managed the Fund since 2006.

Class N Share Purchase. The minimum initial investment for an account generally is $2,500. The minimum subsequent investment generally is $1,000. Certain exceptions to the minimum initial and subsequent investment amounts may apply. See “Your Account—Class N Shares” for additional information on eligibility requirements applicable to purchasing Class N shares.

Class I Share Purchase. The minimum initial investment for an account generally is $500,000 (or any lesser amount if, in William Blair’s opinion, the investor has adequate intent and availability of funds to reach a future level of investment of $500,000). There is no minimum for subsequent purchases. There is no minimum initial investment for qualified retirement plans, including, but not limited to, 401(k) plans, 457 plans, employer-sponsored 403(b) plans, defined benefit plans and other similar accounts, or plans whereby Class I shares are held through omnibus accounts (either at the plan level or the level of the plan administrator) and certain other accounts. William Blair may make certain additional exceptions to the minimum initial investment amount in its discretion. Class I shares are only available to certain investors. See “Your Account—Class I Shares” for additional information on the eligibility requirements and investment minimums applicable to purchasing Class I shares.

held through omnibus accounts (either at the plan level or the level of the plan administrator) and certain other accounts. William Blair may make certain additional exceptions to the minimum initial investment amount in its discretion. Class R6 shares are only available to certain investors. See “Your Account—Class R6 Shares” for additional information on eligibility requirements and investment minimums applicable to purchasing Class R6 shares.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

TAX INFORMATION: The Fund intends to make distributions that may be taxed as ordinary income or capital gains, unless you are investing through a tax-advantaged investment plan. If you are investing through a tax-advantaged investment plan, withdrawals from the tax-advantaged investment plan may be subject to taxes.

PAYMENTS TO BROKER-DEALERS AND OTHER FINANCIAL INTERMEDIARIES: If you purchase shares of the Fund through a broker-dealer or other financial intermediary (such as a bank), the Fund and its related companies may pay the intermediary for the sale of shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your salesperson to recommend the Fund over another investment. Ask your salesperson or visit your financial intermediary’s website for more information.

INVESTMENT OBJECTIVE: The William Blair Large Cap Growth Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of large capitalized (“large cap”) companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of large cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Adviser considers a company to be a large cap company if it has a market capitalization no smaller than the smallest capitalized company included in the Russell 1000^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to large cap companies, but that may have market capitalizations below the market capitalization of the smallest member of the Russell 1000^® Index.

The Russell 1000^® Index is a widely recognized, unmanaged index that measures the performance of the 1,000 largest U.S. companies. The companies in the Russell 1000^® Index are considered representative of large cap companies. The size of companies in the Russell 1000^® Index may change with market conditions. In addition, changes to the composition of the Russell 1000^® Index can change the market capitalization range of the companies included in the index. As of July 1, 2019, the Russell 1000^® Index included securities issued by companies that ranged in size between $1.7 billion and $1,039.7 billion. The Russell 1000^® Growth Index, the Fund’s benchmark, measures the performance of those Russell 1000 companies with a greater-than-average growth orientation.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of large cap U.S. growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

conditions, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. Events such as war, acts of terrorism, social unrest, natural disasters, the spread of infectious illness or other public health threats could also significantly impact the Fund and its investments. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously. Geopolitical and other events may also disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

commenced operations on May 2, 2019. Performance information for Class R6 shares will be provided after a full calendar year of performance history is available. After-tax returns for Class I shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). James S. Golan, a Partner of the Adviser, and David P. Ricci, a Partner of the Adviser, co-manage the Fund. Mr. Golan has co-managed the Fund since 2005. Mr. Ricci has co-managed the Fund since 2011.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Mid Cap Growth Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 43% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of medium capitalized (“mid cap”) companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of mid cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Adviser considers a company to be a mid cap company if it has a market capitalization no smaller than the smallest capitalized company, and no larger than the largest capitalized company, included in the Russell Midcap^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to mid cap companies, but that may have market capitalizations above the market capitalization of the largest member, or below the market capitalization of the smallest member, of the Russell Midcap^® Index.

The Russell Midcap^® Index measures the performance of the 800 companies with the lowest market capitalizations in the Russell 1000^® Index. The companies in the Russell Midcap^® Index are considered representative of mid cap companies. The size of companies in the Russell Midcap^® Index may change with market conditions. In addition, changes to the composition of the Russell Midcap^® Index can change the market capitalization range of companies included in the index. As of July 1, 2019, the Russell Midcap^® Index included securities issued by companies that ranged in size between $1.7 billion and $1,039.7 billion. The Russell Midcap^® Growth Index, the Fund’s benchmark, measures the performance of the smallest 800 companies in the Russell 1000^® Index with a greater-than-average growth orientation.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of mid cap U.S. growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously. Geopolitical and other events may also disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments.

Mid Cap Company Risk. Stocks of mid cap companies involve greater risk than those of larger, more established companies. This is because mid cap companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of mid cap companies may be more volatile and less liquid than securities of large capitalized companies.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

Average Annual Total Returns (For the periods ended December 31, 2019). The table below shows returns on a before-tax and after-tax basis for Class N shares and on a before-tax basis for Class I shares. Class R6 shares commenced operations on May 2, 2019. Performance information for Class R6 shares will be provided after a full calendar year of performance history is available. After-tax returns for Class I shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Daniel Crowe, a Partner of the Adviser, James E. Jones, a Partner of the Adviser, and Robert C. Lanphier IV, a Partner of the Adviser, co-manage the Fund. Mr. Crowe has co-managed the Fund since 2015. Mr. Jones has co-managed the Fund since 2019. Mr. Lanphier has co-managed the Fund since its inception in 2006. Effective September 30, 2020, Mr. Lanphier will retire as a portfolio manager of the Fund.

investment of $1 million). There is no minimum for subsequent purchases. There is no minimum initial investment for qualified retirement plans, including, but not limited to, 401(k) plans, 457 plans, employer-sponsored 403(b) plans, defined benefit plans and other similar accounts, or plans whereby Class R6 shares are held through omnibus accounts (either at the plan level or the level of the plan administrator) and certain other accounts. William Blair may make certain additional exceptions to the minimum initial investment amount in its discretion. Class R6 shares are only available to certain investors. See “Your Account—Class R6 Shares” for additional information on eligibility requirements and investment minimums applicable to purchasing Class R6 shares.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Small-Mid Cap Core Fund (the “Fund”) seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance. For the period October 1, 2019 (commencement of operations) through December 31, 2019, the Fund’s portfolio turnover rate was 12% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES: Under normal circumstances, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small capitalized (“small cap”) and medium capitalized (“mid cap”) companies. The Fund invests in a diversified portfolio of equity securities, primarily common stocks, of small cap and mid cap U.S. companies that the Adviser deems to be of high quality but undervalued by the marketplace. For purposes of the Fund, the Adviser considers a company to be a small cap or a mid cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell Midcap^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics similar to small cap and mid cap companies, but that may have market capitalizations above the market capitalization of the largest member of the Russell Midcap^® Index.

The Russell Midcap^® Index measures the performance of the 800 companies with the lowest market capitalizations in the Russell 1000^® Index. The size of companies in the Russell Midcap^® Index may change with market conditions. In addition, changes to the composition of the Russell Midcap^® Index can change the market capitalization range of companies included in the index As of July 1, 2019, the Russell Midcap^® Index included securities issued by companies that ranged in size between $1.7 billion and $39.4 billion. The Russell 2500^TM Index, the Fund’s benchmark, measures the performance of the 2500 smallest companies in the Russell 3000^® Index with a weighted average market capitalization of approximately $5.2 billion, median capitalization of $1.1 billion and market capitalization of the largest company at $15.0 billion as of July 1, 2019.

In choosing investments, the Adviser performs fundamental company analysis and focuses on stock selection. The Adviser evaluates the extent to which a company meets the criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company should be, or should have the expectation of becoming, a significant provider in the primary markets it serves; (b) the company should have some distinctive attribute relative to present or potential competitors (this may, for example, take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition); and (c) the company should have a strong management team.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of small cap and mid cap U.S. companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Small and Mid Cap Company Risk. Stocks of small and mid cap companies involve greater risk than those of larger, more established companies. This is because small and mid cap companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Small and mid cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of small and mid cap companies may be more volatile and less liquid than securities of large capitalized companies.

New Fund Risk. As a new fund, there can be no assurance that the Fund will grow to or maintain an economically viable size, in which case it could ultimately liquidate.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

The Fund is not intended to be a complete investment program and is designed for long-term investors.

FUND PERFORMANCE HISTORY: Information on the Fund’s annual total returns and average annual total returns will be provided after the Fund has completed a full calendar year of operations. Updated performance information will be available on the Fund’s website at www.williamblairfunds.com or by calling 1-800-635-2886.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Daniel Crowe, a Partner of the Adviser, Robert C. Lanphier IV, a Partner of the Adviser, and Ward D. Sexton, a Partner of the Adviser, co-manage the Fund. Messrs. Crowe, Lanphier, and Sexton have co-managed the Fund since its inception in 2019. Effective September 30, 2020, Mr. Lanphier will retire as a portfolio manager of the Fund.

Class R6 Share Purchase. The minimum initial investment for an account is $1 million (or any lesser amount if, in William Blair’s opinion, the investor has adequate intent and availability of funds to reach a future level of investment of $1 million). There is no minimum for subsequent purchases. There is no minimum initial investment for qualified retirement plans, including, but not limited to, 401(k) plans, 457 plans, employer-sponsored 403(b) plans, defined benefit plans and other similar accounts, or plans whereby Class R6 shares are held through omnibus accounts (either at the plan level or the level of the plan administrator) and certain other accounts. William Blair may make certain additional exceptions to the minimum initial investment amount in its discretion. Class R6 shares are only available to certain investors. See “Your Account—Class R6 Shares” for additional information on eligibility requirements and investment minimums applicable to purchasing Class R6 shares.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Small-Mid Cap Growth Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small capitalized (“small cap”) and medium capitalized (“mid cap”) companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap and mid cap domestic growth companies that are expected to exhibit quality growth characteristics. For purposes of the Fund, the Adviser considers a company to be a small cap or mid cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell Midcap^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to small cap and mid cap companies, but that may have market capitalizations above the market capitalization of the largest member of the Russell Midcap^® Index.

The Russell Midcap^® Index measures the performance of the 800 companies with the lowest market capitalizations in the Russell 1000^® Index. The size of companies in the Russell Midcap^® Index may change with market conditions. In addition, changes to the composition of the Russell Midcap^® Index can change the market capitalization range of companies included in the index. As of July 1, 2019, the Russell Midcap^® Index included securities issued by companies that ranged in size between $1.7 billion and $39.4 billion. The Russell 2500^TM Growth Index, the Fund’s benchmark, measures the performance of those Russell 2500^TM companies with higher price-to-book ratios and higher forecasted growth values. The Russell 2500^TM Index measures the performance of the 2500 smallest companies in the Russell 3000^® Index with a weighted average market capitalization of approximately $5.2 billion, median capitalization of $1.1 billion and market capitalization of the largest company at $15.0 billion as of July 1, 2019.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of small cap and mid cap U.S. growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

infectious illness or other public health threats could also significantly impact the Fund and its investments. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously. Geopolitical and other events may also disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Daniel Crowe, a Partner of the Adviser, James E. Jones, a Partner of the Adviser, and Robert C. Lanphier IV, a Partner of the Adviser, co-manage the Fund. Mr. Crowe has co-managed the Fund since 2015. Mr. Jones has co-managed the Fund since 2019. Mr. Lanphier has co-managed the Fund since its inception in 2003. Effective September 30, 2020, Mr. Lanphier will retire as a portfolio manager of the Fund.

amounts may apply. See “Your Account—Class N Shares” for additional information on eligibility requirements applicable to purchasing Class N shares.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Small-Mid Cap Value Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small capitalized (“small cap”) and medium capitalized (“mid cap”) companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap and mid cap domestic companies that the Adviser believes offer a long-term investment value. For purposes of the Fund, the Adviser considers a company to be a small cap or mid cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell 2500^TM Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase equity securities of companies with business characteristics and value prospects similar to small and mid cap companies, but that may have market capitalizations above the market capitalization of the largest member of the Russell 2500^TM Index.

The Russell 2500^TM Index measures the performance of the 2500 companies with the lowest market capitalizations in the Russell 3000^® Index. The size of companies in the Russell 2500^TM Index may change with market conditions. In addition, changes to the composition of the Russell 2500^TM Index can change the market capitalization range of companies included in the index. As of July 1, 2019, the Russell 2500^TM Index included securities issued by companies that ranged in size between $58.4 million and $15.0 billion. The Russell 2500^TMValue Index, the Fund’s benchmark, measures the performance of those Russell 2500 companies with lower price-to-book ratios and lower forecasted growth values.

In choosing investments, the Adviser performs fundamental company analysis and focuses on stock selection. The Adviser evaluates the extent to which a company meets the following criteria set forth below. All of the criteria are evaluated relative to the valuation of the security. The weight given to a particular investment criterion will depend upon the circumstances, and Fund holdings may not meet all of the following criteria: (a) the company’s current market value should reflect a material discount from the Adviser’s estimate of the company’s value, (b) the company should have some distinctive attribute that cannot easily be duplicated by present or potential competitors (this may take the form of proprietary products or processes, a unique distribution system, an entrenched brand name or an especially strong financial position relative to its competition), (c) the company should have a reasonable expectation of improving its level of profitability, free cash flow, and return on invested capital over a three-year investment horizon, (d) the company should have a capable and skilled management team with a reasonable probability of successfully executing a clearly articulated and logical business strategy focused on creating shareholder value, (e) the company should have a relatively simple, clean financial structure and adhere to conservative and straightforward accounting practices, and (f) there should be the likelihood that management will be able to successfully execute a corporate transformation with a focus on improving cash flow and returns within a three-year investment horizon.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of U.S. small cap and mid cap value companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the value investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

Portfolio Turnover Rate Risk. Higher portfolio turnover rates involve correspondingly higher transaction costs, which are borne directly by the Fund. In addition, the Fund may realize significant short-term and long-term capital gains, which will result in taxable distributions to investors that may be greater than those made by other funds with lower portfolio turnover rates.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the calendar years since the Fund started for Class N shares.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

inception in 2011. Mr. Leslie has co-managed the Fund since its inception in 2011. Mr. Mitchell has co-managed the Fund since its inception in 2011.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Small Cap Growth Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small capitalized (“small cap”) companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap domestic growth companies that are expected to exhibit quality growth characteristics. The Fund’s investments in small cap companies may include a significant weighting to micro-cap companies (which, for purposes of the Fund, are companies with market capitalizations of $1 billion or less at the time of the Fund’s investment). For purposes of the Fund, the Adviser considers a company to be a small cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell 2000^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and growth prospects similar to small cap companies, but that may have market capitalizations above the market capitalization of the largest member of the Russell 2000^® Index.

The Russell 2000^® Index is a widely recognized, unmanaged index of common stocks that measures the performance of the 2,000 smallest companies in the Russell 3000^® Index. The companies in the Russell 2000^® Index are considered representative of small cap companies. The size of companies in the Russell 2000^® Index may change with market conditions. In addition, changes to the composition of the Russell 2000^® Index can change the market capitalization range of the companies included in the index. As of July 1, 2019, the Russell 2000^® Index included securities issued by companies that ranged in size between $58 million and $10.3 billion. The Russell 2000^® Growth Index, the Fund’s benchmark, measures the performance of those Russell 2000 companies with a greater-than-average growth orientation.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of small cap U.S. growth companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Small and Micro Cap Company Risk. Stocks of small and micro cap companies involve greater risk than those of larger, more established companies. This is because small and micro cap companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Small and micro cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of small and micro cap companies may be more volatile and less liquid than securities of large capitalized companies. For purposes of the Fund, micro cap companies are companies with market capitalizations of $1 billion or less at the time of the Fund’s investment.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Michael P. Balkin, a Partner of the Adviser, and Ward D. Sexton, a Partner of the Adviser, co-manage the Fund. Mr. Balkin co-managed the Fund from its inception in 1999 until 2005 and has co-managed the Fund since 2008. Mr. Sexton has co-managed the Fund since 2016.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Small Cap Value Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small capitalized (“small cap”) companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), of small cap domestic companies that the Adviser believes offer a long-term investment value. For purposes of the Fund, the Adviser considers a company to be a small cap company if it has a market capitalization no larger than the largest capitalized company included in the Russell 2000^® Index at the time of the Fund’s investment. Securities of companies whose market capitalizations no longer meet this definition after purchase may continue to be held in the Fund. To a limited extent, the Fund may also purchase stocks of companies with business characteristics and value prospects similar to small cap companies, but that may have market capitalizations above the market capitalization of the largest member of the Russell 2000^® Index.

The Russell 2000^® Index is a widely recognized, unmanaged index of common stocks that measures the performance of the 2,000 smallest companies in the Russell 3000^® Index. The companies in the Russell 2000^® Index are considered representative of small cap companies. The size of companies in the Russell 2000^® Index may change with market conditions. In addition, changes to the composition of the Russell 2000^® Index can change the market capitalization range of the companies included in the index. As of July 1, 2019, the Russell 2000^® Index included securities issued by companies that ranged in size between $58 million and $10.3 billion. The Russell 2000^® Value Index, the Fund’s benchmark, measures the performance of those Russell 2000 companies with lower price-to-book ratios and lower forecasted growth values.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of U.S. small cap value companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Small and Micro Cap Company Risk. Stocks of small and micro cap companies involve greater risk than those of larger, more established companies. This is because small and micro cap companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Small and micro cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of small and micro cap companies may be more volatile and less liquid than securities of large capitalized companies. For purposes of the Fund, micro cap companies are companies with market capitalizations of $500 million or less at the time of the Fund’s investment.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the value investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Chad M. Kilmer, a Partner of the Adviser, Mark T. Leslie, a Partner of the Adviser, and David S. Mitchell, a Partner of the Adviser, co-manage the Fund. Mr. Kilmer has co-managed the Fund since 2006. Mr. Leslie has co-managed the Fund since 2005. Mr. Mitchell has managed or co-managed the Fund since its inception in 1996.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Global Leaders Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its total assets in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes worldwide that the Adviser believes have above-average growth, profitability and quality characteristics. The Adviser seeks investment opportunities in companies at different stages of development, ranging from large, well-established companies to smaller companies at earlier stages of development, that are leaders in their country, industry or globally in terms of products, services or execution. The Fund’s investments are normally allocated among at least six different countries and no more than 65% of the Fund’s equity holdings may be invested in securities of issuers in any one country at any given time. Under normal market conditions, at least 40% of the Fund’s assets will be invested in companies located outside the United States. Normally, the Fund’s investments will be divided among the United States, Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 30% of its net assets or twice the emerging markets component of the MSCI All Country World Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.

In choosing investments, the Adviser performs fundamental company analysis and focuses on stock selection. The Adviser generally seeks equity securities, including common stocks, of companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.

The Adviser will vary the Fund’s sector and geographic diversification based upon the Adviser’s ongoing evaluation of economic, market and political trends throughout the world. In making decisions regarding country allocation, the Adviser will consider such factors as the conditions and growth potential of various economies and securities markets, currency exchange rates, technological developments in the various countries and other pertinent financial, social, national and political factors.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of companies throughout the world, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Foreign Investment Risk. The risks of foreign investments may include less publicly available information, less governmental regulation and supervision of foreign stock exchanges, brokers and issuers, share registration and custody, a lack of uniform accounting, auditing and financial reporting standards, practices and requirements, the possibility of expropriation, seizure or nationalization, confiscatory taxation, limits on repatriation, adverse changes in investment or exchange control regulations, political instability, restrictions on the flow of international capital, imposition of foreign withholding or other taxes, fluctuating currencies, inflation, difficulty in obtaining and enforcing judgments against foreign entities or other adverse political, social or diplomatic developments that could affect the Fund’s investments. Foreign investments may be less liquid and their prices more volatile than the securities of U.S. companies. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations.

Geographic Risk. To the extent that the Fund invests a significant portion of its assets in any one country or geographic region, the Fund will be subject to greater risk of loss or volatility than if the Fund always maintained wide geographic diversity among the countries and geographic regions in which it invests. Investing in any one country or geographic region makes the Fund more vulnerable to the risks of adverse securities markets, exchange rates and social, political, regulatory and economic events in that one country or geographic region.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

Average Annual Total Returns (For the periods ended December 31, 2019). The table below shows returns on a before-tax and after-tax basis for Class N shares and on a before-tax basis for Class I and Class R6 shares. After-tax returns for Class I and Class R6 shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Andrew G. Flynn, a Partner of the Adviser, and Kenneth J. McAtamney, a Partner of the Adviser, co-manage the Fund. Mr. Flynn has co-managed the Fund since 2016. Mr. McAtamney has co-managed the Fund since 2008.

sponsored 403(b) plans, defined benefit plans and other similar accounts, or plans whereby Class R6 shares are held through omnibus accounts (either at the plan level or the level of the plan administrator) and certain other accounts. William Blair may make certain additional exceptions to the minimum initial investment amount in its discretion. Class R6 shares are only available to certain investors. See “Your Account—Class R6 Shares” for additional information on eligibility requirements and investment minimums applicable to purchasing Class R6 shares.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair International Leaders Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes domiciled outside the U.S. that the Adviser believes have above-average growth, profitability and quality characteristics. Under normal market conditions, the Fund typically holds a limited number of securities (i.e., 40-70 securities). The Adviser seeks investment opportunities in companies at different stages of development ranging from large, well-established companies to smaller companies at earlier stages of development, that are leaders in their country, industry or globally in terms of products, services or execution. The Fund’s investments are normally allocated among at least six different countries and no more than 50% of the Fund’s equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund’s investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 40% of its net assets or twice the emerging markets component of the MSCI All Country World Ex-U.S. Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of foreign companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations.

Focus Risk. To the extent that the Fund focuses its investments in particular industries, asset classes or sectors of the economy, any market changes affecting companies in those industries, asset classes or sectors may impact the Fund’s performance. In addition, because the Fund may focus its investments in a limited number of securities, its performance may be more volatile than a fund that invests in a greater number of securities.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the calendar years since the Fund started for Class N shares.

Average Annual Total Returns (For the periods ended December 31, 2019). The table below shows returns on a before-tax and after-tax basis for Class N shares and on a before-tax basis for Class I and Class R6 shares. After-tax returns for Class I and Class R6 shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Simon Fennell, a Partner of the Adviser, and Kenneth J. McAtamney, a Partner of the Adviser, co-manage the Fund. Mr. Fennell has co-managed the Fund since 2013. Mr. McAtamney has co-managed the Fund since its inception in 2012.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair International Growth Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

Example: This example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

The Fund may invest the greater of 35% of its net assets or twice the emerging markets component of the MSCI All Country World Ex-U.S. Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Purchase. The Fund is closed to new investors. Shares are only available to certain investors. In certain circumstances, existing shareholders may be able to open a new Fund account for a different share class. See “Your Account—International Growth Fund, Institutional International Growth Fund, International Small Cap Growth Fund and Emerging Markets Small Cap Growth Fund” for information on eligibility requirements applicable to purchasing shares.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Institutional International Growth Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

Example: This example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its total assets in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by companies of all sizes domiciled outside the U.S. that the Adviser believes have above-average growth, profitability and quality characteristics. The Adviser seeks investment opportunities in companies at different stages of development ranging from large, well-established companies to smaller companies at earlier stages of development. The Fund’s investments are normally allocated among at least six different countries and no more than 50% of the Fund’s equity holdings may be invested in securities of issuers in one country at any given time. Normally, the Fund’s investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 35% of its net assets or twice the emerging markets component of the MSCI All Country World Ex-U.S. Investable Market Index (IMI) (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.

superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years.

Average Annual Total Returns (For the periods ended December 31, 2019). The table below shows returns on a before-tax and after-tax basis. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Purchase. The Fund is closed to new investors. Shares are only available to certain investors. See “Your Account—International Growth Fund, Institutional International Growth Fund, International Small Cap Growth Fund and Emerging Markets Small Cap Growth Fund” for information on eligibility requirements applicable to purchasing shares.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair International Small Cap Growth Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

Example: This example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

issuers in one country at any given time. Normally, the Fund’s investments will be divided among Continental Europe, the United Kingdom, Canada, Japan and the markets of the Pacific Basin. The Fund may invest the greater of 35% of its net assets or twice the emerging markets component of the MSCI All Country World Ex-U.S. Small Cap Index (net) in emerging markets, which include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of foreign small cap companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations.

Small and Micro Cap Company Risk. Stocks of small and micro cap companies involve greater risk than those of larger, more established companies. This is because small and micro cap companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Small and micro cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of small and micro cap companies may be more volatile and less liquid than securities of large capitalized companies. For purposes of the Fund, micro cap are companies with market capitalizations of $500 million or less at the time of the Fund’s investment.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

Average Annual Total Returns (For the periods ended December 31, 2019). The table below shows returns on a before-tax and after-tax basis for Class N shares and on a before-tax basis for Class I and Class R6 shares. After-tax returns for Class I and Class R6 shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Simon Fennell, a Partner of the Adviser, and Andrew G. Flynn, a Partner of the Adviser, co-manage the Fund. Mr. Fennell has co-managed the Fund since 2017. Mr. Flynn has co-managed the Fund since 2013.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Emerging Markets Leaders Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in emerging markets securities. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by emerging market companies of all sizes that the Adviser believes have above-average growth, profitability and quality characteristics. Under normal market conditions, the Fund typically holds a limited number of securities (i.e., 50-80 securities). The Adviser seeks investment opportunities in companies at different stages of development, ranging from large, well-established companies to smaller companies at earlier stages of development, that are leaders in their country, industry or globally in terms of products, services or execution. Emerging market companies, for purposes of the Fund, are companies organized under the laws of an emerging market country or that have securities traded principally on an exchange or over-the-counter in an emerging market country. Currently, emerging markets include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. The Fund’s investments are normally allocated among at least six different countries and no more than 50% of the Fund’s equity holdings may be invested in securities of issuers in one country at any given time.

In choosing investments, the Adviser performs fundamental company analysis and focuses on stock selection. The Adviser generally seeks equity securities, including common stocks, of emerging market companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth at reasonable valuation levels will be the primary focus. Stock selection will take into account both local and global comparisons.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of emerging market companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Foreign Investment Risk. The risks of foreign investments may include less publicly available information, less governmental regulation and supervision of foreign stock exchanges, brokers and issuers, share registration and custody, a lack of uniform accounting, auditing and financial reporting standards, practices and requirements, the possibility of expropriation, seizure or nationalization, confiscatory taxation, limits on repatriation, adverse changes in investment or exchange control regulations, political instability, restrictions on the flow of international capital, imposition of foreign withholding or other taxes, fluctuating currencies, inflation, difficulty in obtaining and enforcing judgments against foreign entities or other adverse political, social or diplomatic developments that could affect the Fund’s investments. Foreign investments may be less liquid and their prices more volatile than the securities of U.S. companies. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. equity securities due to the higher custodial fees associated with foreign securities investments.

Currency Risk. The value of the Fund’s portfolio may be affected by changes in exchange rates or control regulations. If a local currency gains against the U.S. dollar, the value of the security increases in U.S. dollar terms. If a local currency declines against the U.S. dollar, the value of the security decreases in U.S. dollar terms. The currencies of emerging market countries may experience a devaluation relative to the U.S. dollar, and continued devaluations may adversely affect the value of the Fund’s assets denominated in such currencies. Many emerging market countries have experienced substantial rates of inflation for many years, and continued inflation may adversely affect the economies and securities markets of such countries.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations. Many emerging market countries have experienced substantial rates of inflation for many years, and continued inflation may adversely affect the economies and securities markets of such countries.

Share Ownership Concentration Risk. To the extent that a significant portion of the Fund’s shares are held by a limited number of shareholders or their affiliates, there is a risk that the share trading activities of these shareholders could disrupt the Fund’s investment strategies, which could have adverse consequences for the Fund and other shareholders (e.g., by requiring the Fund to sell investments at inopportune times or causing the Fund to maintain larger-than-expected cash positions pending acquisition of investments). In addition, separate accounts managed by the Adviser may invest in the Fund and, therefore, the Adviser at times may have discretionary authority over a significant portion of the assets of the Fund. In such instances, the Adviser’s

decision to make changes to or rebalance its clients’ allocations in the separate accounts may substantially impact the Fund’s performance.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Adviser for the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with that of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class I shares.

Average Annual Total Returns (For the periods ended December 31, 2019). The table below shows returns on a before-tax and after-tax basis for Class N shares and on a before-tax basis for Class I and Class R6 shares. After-tax returns for Class I and Class R6 shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In

some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Todd M. McClone, a Partner of the Adviser, and John C. Murphy, a Partner of the Adviser, co-manage the Fund. Mr. McClone has co-managed the Fund since its inception in 2008. Mr. Murphy has co-managed the Fund since 2016.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Emerging Markets Growth Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

Example: This example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in emerging markets securities. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by emerging market companies of all sizes that the Adviser believes have above-average growth, profitability and quality characteristics. The Adviser seeks investment opportunities in companies at different stages of development ranging from large, well-established companies to smaller companies at earlier stages of development. Emerging market companies, for purposes of the Fund, are companies organized under the laws of an emerging market country or that have securities traded principally on an exchange or over-the-counter in an emerging market country. Currently, emerging markets include every country in the world except the United States, Canada,

Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. The Fund’s investments are normally allocated among at least six different countries and no more than 50% of the Fund’s equity holdings may be invested in securities of issuers in one country at any given time.

In choosing investments, the Adviser performs fundamental company analysis and focuses on stock selection. The Adviser generally seeks equity securities, including common stocks, of emerging market companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations.

Portfolio Turnover Rate Risk. Higher portfolio turnover rates involve correspondingly higher transaction costs, which are borne directly by the Fund. In addition, the Fund may realize significant short-term and long-term capital gains, which will result in taxable distributions to investors that may be greater than those made by other funds with lower portfolio turnover rates.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

Average Annual Total Returns (For the periods ended December 31, 2019). The table below shows returns on a before-tax and after-tax basis for Class N shares and on a before-tax basis for Class I and Class R6 shares. After-tax returns for Class I and Class R6 shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Todd M. McClone, a Partner of the Adviser, and Casey Preyss, a Partner of the Adviser, co-manage the Fund. Mr. McClone has co-managed the Fund since its inception in 2005. Mr. Preyss has co-managed the Fund since 2015.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Emerging Markets Small Cap Growth Fund seeks long-term capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of emerging market small capitalization (“small cap”) companies. The Fund invests primarily in a diversified portfolio of equity securities, including common stocks and other forms of equity investments (e.g., securities convertible into common stocks), issued by emerging market small cap companies that the Adviser believes have above average growth, profitability and quality characteristics. For purposes of the Fund, the Adviser considers a company to be a small cap company if it has a float adjusted market capitalization at the time of purchase no larger than the greater of $3 billion or the largest capitalized company included in the MSCI Emerging Markets Small Cap Index (net). Securities of companies whose float adjusted market capitalizations no longer meet this definition of small cap after purchase may continue to be held in the Fund. Emerging market companies, for purposes of the Fund, are companies organized under the laws of an emerging market country or that have securities traded principally on an exchange or over-the-counter in an emerging market country. Currently, emerging markets include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. The Fund’s investments are normally allocated among at least six different countries and no more than 50% of the Fund’s equity holdings may be invested in securities of issuers in one country at any given time.

In choosing investments, the Adviser performs fundamental company analysis and focuses on stock selection. The Adviser generally seeks equity securities, including common stocks, of emerging market companies that historically have had superior growth, profitability and quality relative to local markets and relative to companies within the same industry worldwide, and that are expected to continue such performance. Such companies generally will exhibit superior business fundamentals, including leadership in their field, quality products or services, distinctive marketing and distribution, pricing flexibility and revenue from products or services consumed on a steady, recurring basis. These business characteristics should be accompanied by management that is shareholder return-oriented and that uses conservative accounting policies. Companies with above-average returns on equity, strong balance sheets and consistent, above-average earnings growth will be the primary focus. Stock selection will take into account both local and global comparisons.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Equity Funds General. Because the Fund invests substantially all of its assets in equity securities of emerging market small cap companies, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Small and Micro Cap Company Risk. Stocks of small and micro cap companies involve greater risk than those of larger, more established companies. This is because small and micro cap companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Small and micro cap companies may be traded in low volumes. This can increase volatility and increase the risk that the Fund will not be able to sell a security on short notice at a reasonable price. The securities of small and micro cap companies may be more volatile and less liquid than securities of large capitalized companies. For purposes of the Fund, micro cap companies are companies with market capitalizations of $500 million or less at the time of the Fund’s investment.

Share Ownership Concentration Risk. To the extent that a significant portion of the Fund’s shares are held by a limited number of shareholders or their affiliates, there is a risk that the share trading activities of these shareholders could disrupt the Fund’s investment strategies, which could have adverse consequences for the Fund and other shareholders (e.g., by requiring the Fund to sell investments at inopportune times or causing the Fund to maintain larger-than-expected cash positions pending acquisition of investments). In addition, separate accounts managed by the Adviser may invest in the Fund and, therefore, the Adviser at times may have discretionary authority over a significant portion of the assets of the Fund. In such instances, the Adviser’s

decision to make changes to or rebalance its clients’ allocations in the separate accounts may substantially impact the Fund’s performance.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The Fund involves a high level of risk and may not be appropriate for everyone. You should only consider it for the aggressive portion of your portfolio.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the calendar years since the Fund started for Class N shares.

Average Annual Total Returns (For the periods ended December 31, 2019). The table below shows returns on a before-tax and after-tax basis for Class N shares and on a before-tax basis for Class I and Class R6 shares. After-tax returns for Class I and Class R6 shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the

“Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Bond Fund seeks to outperform the Bloomberg Barclays U.S. Aggregate Index by maximizing total return through a combination of income and capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

PRINCIPAL INVESTMENT STRATEGIES: Under normal market conditions, the Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in bonds. Other types of income producing securities, such as convertible bonds, hybrid bonds and preferred stock, may also be considered in seeking to achieve the Fund’s investment objective. The Fund’s investments may have variable rates of interest. The Fund invests primarily in U.S. dollar denominated, investment grade fixed income securities. A security is considered to be investment grade if it is rated in one of the highest four categories by at least one nationally recognized statistical rating organization (“Rating Organization”). Up to 5% of the Fund’s net assets may be invested in fixed income securities that at the time of purchase are rated below Baa3/BBB- (commonly referred to as “high yield” or “junk” bonds), provided that the securities are rated “B3/B –” or higher by at least one Rating Organization issuing a rating or, if unrated, if the Adviser deems such securities to be of at least “B3/B –” quality at the time of purchase.

The Fund’s assets will principally be invested in obligations of, or guaranteed by, the U.S. Government, its agencies or instrumentalities; corporate debt securities issued by domestic and foreign companies; and mortgage-backed securities and asset-backed securities, which are debt securities issued by a corporation, trust or custodian, or by a U.S. Government agency or instrumentality, that are collateralized (i.e., secured as to payment of interest and/or principal) by a portfolio or pool of assets, such as mortgages, debit balances on credit card accounts or U.S. Government securities. The Fund may also invest in Rule 144A securities.

The anticipated average duration for the Fund is a range within one year longer or shorter than the average duration of the Bloomberg Barclays U.S. Aggregate Index (the “Benchmark”). As of March 27, 2020, the modified adjusted duration of the Benchmark was 5.59 years. The duration of an instrument is different from the maturity of an instrument in that duration measures the average period remaining until the discounted value of the amounts due (principal and interest) under the instrument are to be paid, rather than the instrument’s stated final maturity. In addition, portfolio duration of five years means that if interest rates increased by one percent, the value of the portfolio would decrease by approximately five percent. For purposes of calculating duration, instruments allowing prepayment will be assigned a prepayment schedule by the Adviser based upon industry experience.

In choosing investments, the Adviser emphasizes individual security selection, as well as shifts in the Fund’s portfolio among market sectors. To a lesser extent, the Adviser actively manages the Fund’s average duration relative to the Benchmark.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Credit Risk. The value of the Fund’s fixed income securities is subject to the ability of the issuers of such securities to make interest payments or principal payment at maturity. The credit ratings of issuers could change and negatively affect the Fund’s share price or yield. The Fund’s investments in below-investment-grade fixed income securities may have additional credit risk. Securities rated below investment grade have speculative characteristics and can be more vulnerable to bad economic news than investment grade securities, which could

lead to a weakened capacity to make principal and interest payments. In some cases, below-investment-grade securities may decline in credit quality or go into default. The Fund’s investments in obligations issued or guaranteed by U.S. Government agencies or instrumentalities may not be backed by the full faith and credit of the United States and may differ in the degree of support provided by the U.S. Government.

Interest Rate Risk. Normally, the values of fixed income securities vary inversely with changes in prevailing interest rates. The value of the Fund’s fixed income securities tends to decrease when interest rates rise and tends to increase when interest rates fall. Securities with longer maturities or durations held by the Fund are generally more sensitive to interest rate changes. As such, securities with longer maturities or durations are usually more volatile than those with shorter maturities or durations. The negative impact on fixed income securities from rising interest rates could be swift and significant and negatively impact the Fund’s net asset value. A rising interest rate environment may also result in periods of increased redemptions from fixed income funds and increased supply in the market due to selling activity to meet redemptions. If the Fund has to liquidate portfolio securities to meet redemptions in such an environment, it may have to do so at disadvantageous times and prices, which could negatively impact the Fund’s net asset value.

Mortgage-Backed/Asset-Backed Securities Risk. The Fund’s investments in mortgage-backed securities and asset-backed securities are subject to prepayment and extension risk. Prepayment of high interest rate mortgage-backed securities and asset-backed securities during times of declining interest rates will tend to lower the return of the Fund and may even result in losses to the Fund if the prepaid securities were acquired at a premium. Slower prepayments during periods of rising interest rates may increase the duration of the Fund’s mortgage-backed securities and asset-backed securities and reduce their value.

Income Risk. The income received by the Fund may decrease as a result of a decline in interest rates.

Foreign Investment Risk. The risks of foreign investments may include less publicly available information, less governmental regulation and supervision of foreign stock exchanges, brokers and issuers, share registration and custody, a lack of uniform accounting, auditing and financial reporting standards, practices and requirements, the possibility of expropriation, seizure or nationalization, confiscatory taxation, limits on repatriation, adverse changes in investment or exchange control regulations, political instability, restrictions on the flow of international capital, imposition of foreign withholding or other taxes, fluctuating currencies, inflation, difficulty in obtaining and enforcing judgments against foreign entities or other adverse political, social or diplomatic developments that could affect the Fund’s investments. Foreign investments may be less liquid and their prices more volatile than the securities of U.S. companies. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. securities due to the higher custodial fees associated with foreign securities investments.

The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

Average Annual Total Returns (For the periods ended December 31, 2019). The table below shows returns on a before-tax and after-tax basis for Class N shares and on a before-tax basis for Class I and Class R6 shares. After-tax returns for Class I and Class R6 shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

For current yield information see: https://www.williamblairfunds.com/funds_and_performance/share_class_n/total_returns.fs

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Paul J. Sularz, an Associate of the Adviser, and Ruta Ziverte, an Associate of the Adviser, co-manage the Fund. Mr. Sularz has co-managed the Fund since 2010. Ms. Ziverte has co-managed the Fund since 2020.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Income Fund seeks a high level of current income with relative stability of principal.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

PRINCIPAL INVESTMENT STRATEGIES: As a matter of fundamental policy, under normal market conditions, the Fund invests at least 90% of its total assets in the following: (a) U.S. dollar-denominated corporate debt securities (domestic or foreign) with long-term ratings of “A –” or better, or an equivalent rating, by at least one of the following three nationally recognized statistical rating organizations: Fitch Ratings, Moody’s Investors Service, Inc. and Standard & Poor’s, a division of The McGraw-Hill Companies, Inc. (“Rating Organizations”); (b) obligations of or guaranteed by the U.S. Government, its agencies or instrumentalities; (c) collateralized obligations, which are debt securities issued by a corporation, trust or custodian, or by a U.S. Government agency or instrumentality, that are collateralized (i.e., secured as to payment of interest and/or principal) by a portfolio or pool of assets, such as mortgages, mortgage-backed securities, debit balances on credit card accounts or U.S. Government securities (the Fund may invest in collateralized obligations that are not guaranteed by a U.S. Government agency or instrumentality only if the collateralized obligations are rated “A –” or better, or an equivalent rating, by one of the Rating Organizations); and (d) commercial paper obligations rated within the highest grade by one of the Rating Organizations. The Fund may also invest in Rule 144A securities.

The Adviser seeks to outperform the Bloomberg Barclays Intermediate Government/Credit Bond Index through an actively managed diversified portfolio of debt securities. The Adviser’s investment philosophy emphasizes shifts in the Fund’s portfolio among various sectors of the debt market, subject to the Fund’s credit quality constraints for its portfolio. The Adviser also actively manages the Fund based upon the average duration and yield to maturity of the Fund’s portfolio and the Adviser’s perceived trends in interest rates.

The anticipated dollar-weighted average maturity of the Fund is three to seven years. The anticipated weighted average modified duration for the Fund is two to five years. The duration of an instrument is different from the maturity of an instrument in that duration measures the average period remaining until the discounted value of the amounts due (principal and interest) under the instrument are to be paid, rather than the instrument’s stated final maturity. In addition, a portfolio duration of five years means that if interest rates increased by one percent, the value of the portfolio would decrease by approximately five percent. Modified duration adjusts duration to take into account the yield to maturity and the number of coupons received each year. For purposes of calculating duration, instruments allowing prepayment will be assigned a prepayment schedule by the Adviser based upon industry experience.

Up to 10% of the Fund’s total assets may be invested in debt securities that at the time of purchase are rated lower than “A –” but at least “BBB –” (or its equivalent) by at least one of the Rating Organizations by which such securities are rated, so long as the Fund does not invest more than 3% of its total net assets in securities of any single issuer whose securities are rated “BBB –”. Securities that are downgraded below “BBB –” (or its equivalent) after purchase may continue to be held in the Fund.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

Credit Risk. The value of the Fund’s fixed income securities is subject to the ability of the issuers of such securities to make interest payments or principal payment at maturity. The credit ratings of issuers could change and negatively affect the Fund’s share price or yield. The Fund’s investments in obligations issued or guaranteed by U.S. Government agencies or instrumentalities may not be backed by the full faith and credit of the United States and may differ in the degree of support provided by the U.S. Government.

Mortgage-Backed/Asset-Backed Securities Risk. The Fund’s investments in mortgage-backed securities and asset-backed securities (including collateralized mortgage obligations) are subject to prepayment and extension risk. Prepayment of high interest rate mortgage-backed securities and asset-backed securities during times of declining interest rates will tend to lower the return of the Fund and may even result in losses to the Fund if the prepaid securities were acquired at a premium. Slower prepayments during periods of rising interest rates may increase the duration of the Fund’s mortgage-backed securities and asset-backed securities and reduce their value.

Income Risk. The income received by the Fund may decrease as a result of a decline in interest rates.

Foreign Investment Risk. The risks of foreign investments may include less publicly available information, less governmental regulation and supervision of foreign stock exchanges, brokers and issuers, share registration and custody, a lack of uniform accounting, auditing and financial reporting standards, practices and requirements, the possibility of expropriation, seizure or nationalization, confiscatory taxation, limits on repatriation, adverse changes in investment or exchange control regulations, political instability, restrictions on the flow of international capital, imposition of foreign withholding or other taxes, fluctuating currencies, inflation, difficulty in obtaining and enforcing judgments against foreign entities or other adverse political, social or diplomatic developments that could affect the Fund’s investments. Foreign investments may be less liquid and their prices more volatile than the securities of U.S. companies. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. securities due to the higher custodial fees associated with foreign securities investments.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

For current yield information see:https://www.williamblairfunds.com/funds_and_performance/share_class_n/total_returns.fs

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Ruta Ziverte, an Associate of the Adviser, manages the Fund. Ms. Ziverte has managed the Fund since 2020.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

INVESTMENT OBJECTIVE: The William Blair Low Duration Fund seeks to maximize total return. Total return includes both income and capital appreciation.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 183% of the average value of its portfolio.

PRINCIPAL INVESTMENT STRATEGIES: The Fund seeks to maximize total return by investing in a diversified portfolio of investment grade low duration debt securities. Total return includes both income and capital appreciation. The Fund seeks to outperform the ICE BofAML 1-Year US Treasury Note Index through an actively managed diversified portfolio of securities. The Adviser actively manages the Fund’s average duration relative to the ICE BofAML 1-Year US Treasury Note Index.

The Fund invests primarily in investment grade debt securities rated in the highest three categories by at least one nationally recognized statistical rating organization.

The Fund invests in U.S. dollar-denominated securities. The Fund’s assets will principally be invested in the following: (1) obligations of or guaranteed by the U.S. Government, its agencies or instrumentalities; (2) corporate debt securities issued by domestic or foreign companies; (3) mortgage-backed securities and asset-backed securities, which are debt securities issued by a corporation, trust or custodian, or by a U.S. Government agency or instrumentality, that are collateralized (i.e., secured as to payment of interest and/or principal) by a portfolio or pool of assets, such as mortgages, debit balances on credit card accounts or U.S. Government securities; and (4) money market instruments, including, but not limited to, those issued by domestic companies, the U.S. Government and its agencies and instrumentalities, U.S. banks and municipalities. The Fund may also invest in Rule 144A securities.

The anticipated weighted average duration for the Fund is between 0 to 3 years. The duration of an instrument is different from the maturity of an instrument in that duration measures the average period remaining until the discounted value of the amounts due (principal and interest) under the instrument are to be paid, rather than the instrument’s stated final maturity. In addition, portfolio duration of two years means that if interest rates increased by one percent, the value of the portfolio would decrease by approximately two percent. For purposes of calculating duration, instruments allowing prepayment will be assigned a prepayment schedule by the Adviser based upon industry experience.

The Fund may also invest in U.S. dollar-denominated money market instruments issued by foreign banks, foreign governments and multinational organizations, such as the World Bank. The Fund may also invest in Section 4(2) commercial paper.

PRINCIPAL RISKS: The Fund’s returns will vary, and you could lose money by investing in the Fund. The following is a summary of the principal risks associated with an investment in the Fund.

by U.S. Government agencies or instrumentalities may not be backed by the full faith and credit of the United States and may differ in the degree of support provided by the U.S. Government.

Income Risk. The income received by the Fund may decrease as a result of a decline in interest rates.

Foreign Investment Risk. The risks of foreign investments may include less publicly available information, less governmental regulation and supervision of foreign stock exchanges, brokers and issuers, share registration and custody, a lack of uniform accounting, auditing and financial reporting standards, practices and requirements, the possibility of expropriation, seizure or nationalization, confiscatory taxation, limits on repatriation, adverse changes in investment or exchange control regulations, political instability, restrictions on the flow of international capital, imposition of foreign withholding or other taxes, fluctuating currencies, inflation, difficulty in obtaining and enforcing judgments against foreign entities or other adverse political, social or diplomatic developments that could affect the Fund’s investments. Foreign investments may be less liquid and their prices more volatile than the securities of U.S. companies. The Fund is expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. securities due to the higher custodial fees associated with foreign securities investments.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with that of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the last ten calendar years for Class N shares.

Average Annual Total Returns (For the periods ended December 31, 2019). The table below shows returns on a before-tax and after-tax basis for Class N shares and on a before-tax basis for Class I and Class R6 shares. After-tax returns for Class I and Class R6 shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

For current yield information see:https://www.williamblairfunds.com/funds_and_performance/share_class_n/total_returns.fs

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Paul J. Sularz, an Associate of the Adviser, and Kathleen M. Lynch, an Associate of the Adviser, co-manage the Fund. Mr. Sularz has co-managed the Fund since its inception in 2009. Ms. Lynch has co-managed the Fund since 2020.

Sale. Shares of the Fund are redeemable on any day the New York Stock Exchange is open for business by mail, wire or telephone, depending on the elections you make in the account application.

The Growth Fund, the Large Cap Growth Fund, the Mid Cap Growth Fund, the Small-Mid Cap Core Fund, the Small-Mid Cap Growth Fund, the Small-Mid Cap Value Fund, the Small Cap Growth Fund, the Small Cap Value Fund, the Global Leaders Fund, the International Leaders Fund, the International Growth Fund, the Institutional International Growth Fund, the International Small Cap Growth Fund, the Emerging Markets Leaders Fund, the Emerging Markets Growth Fund and the Emerging Markets Small Cap Growth Fund each seek long-term capital appreciation.

The Bond Fund seeks to outperform the Bloomberg Barclays U.S. Aggregate Index by maximizing total return through a combination of income and capital appreciation.

The Income Fund seeks a high level of current income with relative stability of principal.

The Low Duration Fund seeks to maximize total return. Total return includes both income and capital appreciation.

The Summary Sections describe each Fund’s principal investment policies and strategies intended to achieve each Fund’s investment objective. The investment types detailed in each Fund’s Summary Section are further described in the Investment Glossary included in this prospectus and in the Statement of Additional Information. For each Fund with an 80% investment policy, the Fund will provide shareholders with at least 60 days’ notice of any changes to its 80% investment policy. For the avoidance of doubt, in appropriate circumstances, synthetic instruments, such as derivatives, and other investment companies may count toward the Fund’s 80% investment policy if those instruments have economic characteristics similar to the other investments included in the 80% policy.

Forward Foreign Currency Transactions. A forward foreign currency contract is an agreement to purchase or sell a specific currency at a specified future date and price agreed to by the parties at the time of entering into the contract. A Fund will not engage in forward currency contracts in which the specified future date is more than one year from the time of entering into the contract. A Fund will not enter into a forward currency contract if such contract would obligate the Fund to deliver an amount of foreign currency in excess of the value of the Fund’s securities or other assets denominated in that currency.

Futures, Options and Swaps. The Bond Fund, the Income Fund and the Low Duration Fund may use futures, options and swaps to hedge against movements in interest rates and credit spreads and to manage duration. Specifically, the Fund may purchase or sell futures contracts on U.S. Treasury securities, buy options on futures and enter into credit default swaps on a credit default swap index.

Mortgage-Backed TBAs. The Bond Fund, the Income Fund and the Low Duration Fund may purchase and sell mortgage-backed to-be-announced (TBA) securities to hedge against movements in interest rates and for risk management purposes. Purchase and sale of TBA securities may cause a Fund’s portfolio turnover rate to appear higher. See “Portfolio Turnover” below

The Investment Glossary included in this prospectus and the Statement of Additional Information contain additional information regarding the investment types described above.

Temporary Defensive Position. Each Fund may significantly alter its make-up as a temporary defensive strategy. A defensive strategy will be employed only if, in the judgment of the Adviser, investments in a Fund’s usual markets or types of securities become decidedly unattractive because of current or anticipated adverse economic, financial, political and social factors. For temporary defensive purposes, a Fund may invest up to 100% of its assets in other types of securities, including high-quality commercial paper, obligations of banks and savings institutions, U.S. Government securities, government agency securities and repurchase agreements, or it may retain funds in cash. When a Fund is invested defensively, it may not meet its investment objective.

Use of Derivatives and ETFs for Managing Large Fund Flows. Each Fund may use derivative instruments and securities of other investment companies such as exchange-traded funds (“ETFs”) to equitize cash in situations involving large cash inflows or anticipated large redemptions. Derivatives are financial contracts whose value depends on, or is derived from, the value of an underlying asset, reference rate or index. Investing in derivatives involves investment techniques and risks different from those associated with ordinary mutual fund securities transactions and may involve increased transaction costs. Each Fund’s investment in derivatives may rise or fall more rapidly in value than other investments and may reduce each Fund’s returns. Changes in the value of the derivative may not correlate perfectly, or at all, with the underlying asset, reference rate or index, and each Fund could lose more than the principal amount invested. Derivatives also may be subject to certain other risks such as leveraging risk, liquidity risk, interest rate risk, market risk, credit risk, counterparty risk, management risk and the risk of mispricing or improper valuation. Derivatives also may not behave as anticipated, especially in abnormal market conditions. The use of derivatives may increase the volatility of a Fund’s net asset value. Derivatives are subject to fees and other costs which are not reflected in the Annual Fund Operating Expenses table. Each Fund may also use derivatives for risk management and hedging purposes, as discussed further in the Statement of Additional Information.

The risks of investment in other investment companies typically reflect the risk of the types of securities in which the other investment companies invest. Investments in ETFs are subject to the additional risk that shares of the ETF may trade at a premium or discount to their net asset value per share. When a Fund invests in another investment company, shareholders of the Fund bear their proportionate share of the other investment company’s fees and expenses as well as their share of the Fund’s fees and expenses. There may also not be an active trading market available for shares of some ETFs. Additionally, trading of ETF shares may be halted and ETF shares may be delisted by the listing exchange.

Portfolio Turnover. No Fund intends to trade portfolio securities for the purpose of realizing short-term profits. However, each Fund will adjust its portfolio as considered advisable in view of prevailing or anticipated market conditions and the Fund’s investment objective, and there is no limitation on the length of time securities must be held by the Fund prior to being sold. Portfolio turnover rate will not be a limiting factor for a Fund. The Small-Mid Cap Value Fund, Small Cap Value Fund, Emerging Markets Small Cap Growth Fund, Income Fund and Low Duration Fund each had a portfolio turnover rate at or higher than 100% for the year ended December 31, 2019. Higher portfolio turnover rates involve correspondingly higher transaction costs, which are borne directly by a Fund. In addition, a Fund may realize significant short-term and long-term capital gains, which will result in taxable distributions to investors that may be greater than those made by other funds with lower portfolio turnover rates. Tax and transaction costs may lower a Fund’s effective return for investors. Notwithstanding the foregoing, with respect to the Bond Fund, Income Fund and Low Duration Fund, the transaction costs incurred in connection with rolling over positions in TBA securities are expected to be minimal.

Portfolio Holdings. A description on the policies and procedures with respect to the disclosure of each Fund’s portfolio securities is available in the Statement of Additional Information.

Additional Information About the Funds. Each Fund is a series of William Blair Funds, an open-end management investment company. The Adviser provides management and investment advisory services to the Funds. This prospectus doesn’t tell you about every policy or risk of investing in each Fund. If you want more information on each Fund’s allowable securities and investment practices and the characteristics and risks of each one, you may want to request a copy of the Statement of Additional Information (the back cover tells you how to do this).

Each Fund’s principal risks are summarized in the Fund’s Summary section. The following provides additional detail about certain of those risks and additional principal risks of each Fund.

Equity Funds General. Because each equity Fund invests substantially all of its assets in equity securities, the primary risk is that the value of the equity securities it holds might decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, a Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected or a strategy used by the Adviser may fail to produce its intended result.

Market Risk. The value of the Fund’s investments may go up or down, sometimes rapidly or unpredictably. The value of an investment may decline due to factors affecting securities markets generally or particular industries represented in the securities markets. The value of an investment may decline due to general market conditions that are not specifically related to a particular company, such as real or perceived adverse economic conditions, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. Furthermore, local, regional and global events such as war, acts of terrorism, social unrest, natural disasters, the spread of infectious illness or other public health threats could also adversely impact issuers, markets and economies, including in ways that cannot necessarily be foreseen. The Fund could be negatively impacted if the value of a portfolio holding were harmed by such political or economic conditions or events. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously.

Style Risk. Different investment styles (e.g., growth vs. value, quality bias, market capitalization focus) tend to shift in and out of favor depending on market conditions and investor sentiment, and at times when the investment style used by the Adviser for a Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

Smaller Company Risk. Stocks of smaller companies involve greater risk than those of larger, more established companies. This is because smaller companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Smaller companies may be more adversely affected by poor economic or market conditions, and may be traded in low volumes, which may increase volatility and liquidity risks. From time to time, each of the Funds that invest in small cap stocks may invest in the equity securities of very small cap companies, often referred to as “micro-cap” companies. For purposes of the Funds, “micro-cap” companies are those with market capitalizations of $500 million or less at the time of a Fund’s investment (except for the U.S. equity growth Funds, for which “micro-cap” companies are those with market capitalizations of $1 billion or less at the time of a Fund’s investment). The considerations noted above are generally intensified for these investments. Any convertible debentures issued by small cap companies are likely to be lower-rated or non-rated securities, which generally involve more credit risk than debentures in the higher rating categories and generally include some speculative characteristics, including uncertainties or exposure to adverse business, financial or economic conditions that could lead to inadequate capacity to meet timely interest and principal payments.

For the fixed income funds, liquidity risk may be magnified in a rising interest rate environment if redemptions from fixed income funds increase. Increased redemptions from fixed income funds may result in increased supply in the market due to selling activity to meet redemptions. If a Fund has to liquidate portfolio securities to meet redemptions in such an environment, it may have to do so at disadvantageous times and prices, which could negatively impact the Fund’s net asset value. If dealer capacity in fixed income markets is insufficient for market conditions, it may further inhibit liquidity and increase volatility in the fixed income markets.

Focus Risk. To the extent that a Fund focuses its investments in particular industries, asset classes or sectors of the economy, any market price movements, regulatory or technological changes, or economic conditions affecting companies in those industries, asset classes or sectors may have a significant impact on the Fund’s performance. For example, consumer goods companies could be hurt by a rise in unemployment or technology companies could be hurt by such factors as market saturation, price competition and rapid obsolescence.

For the International Leaders Fund and the Emerging Markets Leaders Fund, because each Fund may focus its investments in a limited number of securities, its performance may be more volatile than a fund that invests in a greater number of securities. If securities in which these Funds invest perform poorly, the Funds could incur greater losses than they would have had they invested in a greater number of securities.

Valuation Risk. In certain circumstances, portfolio securities may be valued using techniques other than market quotations, including using fair value pricing. Portfolio securities that are valued using such techniques may be subject to greater fluctuation in their value from one day to the next than would be the case if market quotations were used. In addition, there is no assurance that a Fund could sell a portfolio security for the value established for it at any time, and it is possible that a Fund could incur a loss because a portfolio security is sold for a lower value than its established value.

Share Ownership Concentration Risk. To the extent that a significant portion of a Fund’s shares are held by a limited number of shareholders or their affiliates, there is a risk that the share trading activities of these shareholders could disrupt the Fund’s investment strategies, which could have adverse consequences for the Fund and other shareholders (e.g., by requiring the Fund to sell investments at inopportune times or causing the Fund to maintain larger-than-expected cash positions pending acquisition of investments). In addition, separate accounts managed by the Adviser may invest in the Emerging Markets Leaders Fund, Emerging Markets Growth Fund, and Emerging Markets Small Cap Growth Fund and, therefore, the Adviser at times may have discretionary authority over a significant portion of the assets of a Fund. In such instances, the Adviser’s decision to make changes or rebalance its clients’ allocations in the separate accounts may substantially impact the Fund’s performance.

Foreign Investment Risk. The risks of investing in securities of foreign issuers may include less publicly available information, less governmental regulation and supervision of foreign stock exchanges, brokers and issuers, share registration and custody, a lack of uniform accounting, auditing and financial reporting standards, practices and requirements, the possibility of expropriation, seizure or nationalization, confiscatory taxation, trade restrictions (including tariffs), limits on repatriation, adverse changes in investment or exchange control regulations, political instability, restrictions on the flow of international capital, imposition of foreign withholding and other taxes, fluctuating currencies, inflation, difficulty in obtaining and enforcing judgments against foreign entities or other adverse political, social or diplomatic developments that could affect a Fund’s investments. Securities of some foreign issuers are less liquid and their prices more volatile than the securities of U.S. companies. In addition, the time period for settlement of transactions in certain foreign markets generally is longer than for U.S. markets.

Foreign securities held by a Fund usually will be denominated in currencies other than the U.S. dollar. Therefore, changes in foreign exchange rates will affect the value of the securities held by a Fund either beneficially or adversely. Fluctuations in foreign currency exchange rates will also affect the dollar value of dividends and interest earned, gains and losses realized on the sale of securities and net investment income and gains, if any, available for distribution to shareholders.

Currency Risk. The value of a Fund’s portfolio may be affected by changes in exchange rates or control regulations. If a local currency gains against the U.S. dollar, the value of the security increases in U.S. dollar terms. If a local currency declines against the U.S. dollar, the value of the security decreases in U.S. dollar terms.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations. Certain of these countries have in the past failed to recognize private property rights and have at times nationalized and expropriated the assets of private companies. Political, social and economic structures in many emerging market countries may be less established than in developed countries and may change rapidly. Such countries may also lack the social, political and economic characteristics of more developed countries. Unanticipated political, social or economic developments may affect the values of a Fund’s investments in emerging market countries and the availability to a Fund of additional investments in these countries.

The currencies of certain emerging market countries have from time to time experienced a steady devaluation relative to the U.S. dollar, and continued devaluations may adversely affect the value of a Fund’s assets denominated in such currencies. Many emerging market countries have experienced substantial rates of inflation for many years, and continued inflation may adversely affect the economies and securities markets of such countries.

The small size, limited trading volume and relative inexperience of the financial markets in these countries may make a Fund’s investments in such countries illiquid and more volatile than investments in more developed countries. There may be little financial or accounting information available with respect to issuers located in these countries, and it may be difficult as a result to assess the value or prospects of an investment in such issuers.

The system of share registration and custody in some emerging market countries may create certain risks of loss (including in some cases the risk of total loss) and a Fund may be required to establish special custodial or other arrangements before making investments in these countries. There is an increased risk of uninsured loss due to lost, stolen or counterfeit stock certificates or unauthorized trading, or other fraudulent activity.

Prior governmental approval of non-U.S. investments may be required and foreign investment in U.S. companies may be subject to limitation in some emerging market countries. Foreign ownership limitations also may be imposed by the charters of individual companies in emerging market countries to prevent, among other concerns, violation of foreign investment limitations. Repatriation of investment income, capital and proceeds of sales by foreign investors may require governmental registration and/or approval in some developing countries. A Fund could be adversely affected by delays in or a refusal to grant any required governmental registration or approval for such repatriation.

The economies of certain developing countries may be dependent upon international trade and, accordingly, have been and may continue to be adversely affected by trade barriers, exchange controls, managed adjustments in relative currency values and other protectionist measures imposed or negotiated by the countries with which they trade. These economies also have been and may continue to be adversely affected by economic conditions in the countries with which they trade.

Risks of Investing in Russia. The United States and European Union have instituted various sanctions against certain Russian officials. These sanctions and other intergovernmental actions that may be undertaken against Russia may result in the devaluation of Russian currency, a downgrade in the country’s credit rating, and a decline in the value and liquidity of Russian stocks. These sanctions could result in the immediate freeze of Russian securities, impairing the ability of a Fund to buy, sell, receive or deliver those securities. In addition, retaliatory action by the Russian government could involve the seizure of assets and any such actions are likely to impair the value and liquidity of such assets. Any or all of these potential results could harm Russia’s economy. These sanctions, and the continued disruption of the Russian economy, could have a negative effect on the performance of a Fund.

Risks of Investing through China Stock Connect. China A-shares (“A-shares”) are equity securities of companies based in mainland China that trade on Chinese stock exchanges such as the Shanghai Stock Exchange (“SSE”) and the Shenzhen Stock Exchange (“SZSE”). Foreign investment in A-shares on the SSE and SZSE has historically not been permitted, other than through a license granted under regulations in the People’s Republic of China known as the Qualified Foreign Institutional Investor and Renminbi Qualified Foreign Institutional Investor systems. Each license permits investment in A-shares only up to a specified quota.

Investment in eligible A-shares listed and traded on the SSE or the SZSE is also permitted through the respective Shanghai-Hong Kong and Shenzhen-Hong Kong Stock Connect programs (together, “Stock Connect”). Stock Connect is a securities trading and clearing links program developed by Hong Kong Exchanges and Clearing Limited (“HKEX”), SSE, SZSE, and China Securities Depositary and Clearing Corporation Limited (“ChinaClear”) with an aim to achieve mutual stock market access between the People’s Republic of China and Hong Kong.

Investment in eligible A-shares through Stock Connect is subject to trading, clearance and settlement procedures that could pose risks to a Fund. Stock Connect imposes daily quota limitations, and investors may not purchase and sell the same security on the same trading day, which may restrict the Funds’ ability to enter into or exit trades on a timely basis. Stock Connect can operate only when the Shanghai or Shenzhen markets, in addition to the Hong Kong market, are open for trading and when banking services are available in both markets on the corresponding settlement days. As such, if one or both markets are closed on a U.S. trading day, the Funds may not be able to dispose of its A-shares in a timely manner, which could adversely affect Fund performance. HKEX, SSE, and SZSE each reserve the right to suspend trading and the A-shares market has historically had a higher propensity for trading suspensions than many other global equity markets. Because of the way in which A-shares are held in Stock Connect, a Fund may not be able to exercise the rights of a shareholder and may be limited in their ability to pursue claims against the issuer of a security.

The regulations of Stock Connect are relatively new and untested and are subject to changes, which could adversely impact the Funds’ rights with respect to its A-shares. As Stock Connect is relatively new, there are no assurances that the operational systems of the relevant market participants comprising the Stock Connect program will function properly, independently or in coordination with other participants.

Geographic Risk. Although the Funds investing primarily in foreign securities currently intend to maintain geographic diversification, the Funds have the flexibility to invest no more than 50% (65% for Global Leaders Fund) of their equity holdings in securities of issuers in any one country. To the extent that a Fund invests a significant portion of its assets in any one country or geographic region, the Fund will be subject to greater risk of loss or volatility than if the Fund always maintained wide geographic diversity among the countries or geographic regions in which it invests. Investing in any one country or geographic region makes a Fund more vulnerable to the risks of adverse securities markets, exchange rates and social, political, regulatory and economic events in that one country or geographic region.

Geopolitical Risk. Geopolitical and other events may disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of a Fund’s investments. War, terrorism, economic uncertainty, and related geopolitical events have led, and in the future may lead, to increased short-term market volatility and may have adverse long-term effects on U.S. and world economies and markets generally. Likewise, natural and environmental disasters, such as the earthquake and tsunami in Japan in early 2011, and systemic market dislocations of the kind surrounding the insolvency of Lehman Brothers in 2008, if repeated, would be highly disruptive to economies and markets, adversely affecting individual companies and industries, securities markets, interest rates, credit ratings, inflation, investor sentiment, and other factors affecting the value of a Fund’s investments. The United Kingdom (the “UK”) withdrew from the European Union (the “EU”) in January 2020, commonly referred to as “Brexit.” Uncertainty surrounding the withdrawal process and the consequences of Brexit could result in economic, market, and currency instability and volatility in the UK, Europe and

worldwide. Additional members of the EU could pursue similar procedures to withdraw from the EU, increasing the risk of such instability and volatility.

During global market disruptions, a Fund’s exposure to the risks described elsewhere in this Prospectus will likely increase. Market disruptions can also prevent a Fund from implementing its investment strategies for a period of time and achieving its investment objective. For example, a market disruption may adversely affect the orderly functioning of the securities markets and may cause a Fund’s derivatives counterparties to discontinue offering derivatives on some underlying securities, reference rates, or indices, or to offer them on a more limited basis.

Derivatives Risk. Investing in derivatives involves investment techniques and risks different from those associated with ordinary mutual fund securities transactions and may involve increased transaction costs. The Fund’s investment in derivatives may rise or fall more rapidly in value than other investments and may reduce the Fund’s returns. Changes in the value of the derivative may not correlate perfectly, or at all, with the underlying asset, reference rate or index, and the Fund could lose more than the principal amount invested. Derivatives also may be subject to certain other risks such as leveraging risk, liquidity risk, interest rate risk, market risk, credit risk, counterparty risk, management risk and the risk of mispricing or improper valuation. Derivatives also may not behave as anticipated by the Fund, especially in abnormal market conditions. The use of derivatives may increase the volatility of the Fund’s net asset value. Derivatives may be leveraged such that a small investment in derivative securities can have a significant impact on the Fund’s exposure to stock market values, interest rates, currency exchange rates or other investments. As a result, a relatively small price movement in a derivatives contract may cause an immediate and substantial loss or gain. It may be difficult or impossible for the Fund to purchase or sell certain derivatives in sufficient amounts to achieve the desired level of exposure, which may result in a loss or may be costly to the Fund. In addition, the possible lack of a liquid secondary market for certain derivatives and the resulting inability of the Fund to sell or otherwise close out a derivatives position could expose the Fund to losses and could make such derivatives more difficult for the Fund to value accurately. Some derivatives are more sensitive to market price fluctuations and to interest rate changes than other investments. The Fund also could suffer losses related to its derivatives positions as a result of unanticipated market movements, which losses are potentially unlimited. The Fund also may be exposed to losses if the counterparty in the transaction does not fulfill its contractual obligation. In addition, derivatives traded over-the-counter (“OTC derivatives”) do not benefit from the protections provided by exchanges in the event that a counterparty is unable to fulfill its contractual obligation. Such OTC derivatives therefore involve greater counterparty and credit risk and may be more difficult to value than exchange-traded derivatives. When a derivative is used as a hedge against a position that the Fund holds, any loss generated by the derivative should generally be offset by gains on the hedged instrument, and vice versa. While hedging can reduce or eliminate losses, it also can reduce or eliminate gains. Hedges are sometimes subject to imperfect matching between the derivative and the hedged investment, and there can be no assurance that the Fund’s hedging transactions will be effective. Also, suitable derivative transactions may not be available in all circumstances. Derivatives are subject to fees and other costs which are not reflected in the Annual Fund Operating Expenses table.

Derivatives are also subject to liquidity risk. Liquidity risk is the risk that a derivative instrument cannot be sold, closed out or replaced quickly at or very close to its fundamental value. Generally, exchange-traded derivatives are very liquid because the exchange clearinghouse is the counterparty of every contract. OTC derivatives are less liquid than exchange-traded derivatives since they often can be closed out only with the other party to the transaction. The Fund’s ability to sell or close out a position in an instrument prior to expiration or maturity depends on the existence of a liquid secondary market or, in the absence of such a market, the ability and willingness of the counterparty to enter into a transaction closing out the position. Therefore, there is no assurance that any derivatives position can be sold or closed out at a time and price that is favorable to the Fund.

Operating Expenses Risk. The Funds investing primarily in foreign securities are expected to incur operating expenses that are higher than those of mutual funds investing exclusively in U.S. securities because expenses such as custodial fees related to foreign investments are usually higher than those associated with investments in U.S. securities. The Funds sell and redeem shares in U.S. dollars and there are costs associated with converting

holdings in foreign currencies to U.S. dollars. In addition, dividends and interest from foreign securities may be subject to foreign withholding taxes. (For more information, see “Your Account—Federal Income Taxes.”)

Interest Rate Risk. Normally, the values of fixed income securities vary inversely with changes in prevailing interest rates. The value of a Fund’s fixed income securities tends to decrease when interest rates rise and tends to increase when interest rates fall. Securities with longer maturities or durations held by a Fund are generally more sensitive to interest rate changes. As such, securities with longer maturities or durations are usually more volatile than those with shorter maturities or durations. Very low or negative interest rates may magnify interest rate risk for the markets as a whole and for a Fund. A Fund’s investment in variable rate securities will generally be less sensitive to interest rate changes, but such securities may decline in value if their interest rates do not rise as much, or as quickly, as interest rates in general. The negative impact on fixed income securities from rising interest rates could be swift and significant and negatively impact the Fund’s net asset value.

Credit Risk. The value of a Fund’s securities is subject to the ability of the issuers of such securities to make interest payments or payment at maturity. Obligations that are unrated are not necessarily of lower quality than those that are rated, but may be less marketable. Not all securities issued or guaranteed by agencies or instrumentalities of the U.S. Government are backed by the full faith and credit of the United States. Such securities involve different degrees of government backing. Some obligations issued or guaranteed by U.S. Government agencies or instrumentalities in which a Fund may invest are backed by the full faith and credit of the United States, such as modified pass-through certificates issued by the Government National Mortgage Association, while others are backed exclusively by the agency or instrumentality with limited rights of the issuer to borrow from the U.S. Treasury. Others are backed only by the credit of the issuer itself. While the U.S. Government may provide financial support to such agencies or instrumentalities, no assurance can be given that it will always do so since it is not so obligated by law.

A Fund’s investments in below-investment-grade securities (e.g., “high yield” or “junk” bonds) may have additional credit risk. Securities rated below BBB by a nationally recognized statistical rating organization have speculative characteristics and can be more vulnerable to bad economic news than investment grade securities, which could lead to a weakened capacity to make principal and interest payments. In some cases, below-investment-grade securities may decline in credit quality or go into default. For a description of ratings, see Appendix B in the Statement of Additional Information.

Mortgage-Backed/Asset-Backed Securities Risk. The value of a Fund’s mortgage-backed or asset-backed securities may be affected by, among other things, changes in interest rates, factors concerning the interests in and structure of the issuer or the originator of the mortgages, the creditworthiness of the entities that provide any supporting letters of credit, surety bonds or other credit enhancements or the market’s assessment of the quality of underlying assets. During periods of rising interest rates, property owners may prepay their mortgages more slowly than expected, resulting in slower prepayments of mortgage-backed securities, which increases the duration of a security and may reduce its value. When interest rates decline, property owners may prepay their mortgages more quickly than expected. This can reduce the returns of a Fund because the Fund may have to reinvest that money at the lower prevailing interest rates. A Fund’s investments in other asset-backed securities are subject to similar extension and prepayment risks as those described above for mortgage-backed securities.

Income Risk. Income risk is the risk that the income received by the Fund may decrease as a result of a decline in interest rates. A Fund’s income is based on short-term interest rates, which may fluctuate over short periods of time.

Credit Default Swap Risk. Credit default swaps are subject to the credit risk of the underlying reference obligation and to counterparty credit risk. If the counterparty fails to meet its obligations, a Fund may lose money. Credit default swaps are also subject to the risk that the Adviser will not properly assess the risk of the underlying reference obligation. If a Fund is selling credit protection, there is a risk that a credit event will occur and that a Fund will have to pay the counterparty. If a Fund is buying credit protection, there is a risk that no credit event will occur and a Fund will receive no benefit for the premium paid. Credit default swaps may be difficult to value and may have the effect of leverage on a Fund.

Mortgage-Backed To-Be-Announced (TBA) Securities Risk. To the extent a Fund purchases or sells mortgage-backed to-be-announced (TBA) securities, a Fund is subject to the risk that the counterparty may fail to consummate the transaction, which could cause a Fund to miss the opportunity to obtain a price or yield considered to be advantageous. Mortgage-backed TBAs may also have a leverage-like effect on a Fund and may cause a Fund to be more volatile.

Operational and Technology Risk. Cyber-attacks, disruptions, or failures that affect a Fund’s service providers or counterparties, issuers of securities held by the Fund, or other market participants may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Cyber-attacks may include unauthorized attempts by third parties to improperly access, modify, disrupt the operations of, or prevent access to the systems of a Fund’s service providers or counterparties, issuers of securities held by the Fund or other market participants or data within them. In addition, power or communications outages, acts of god, information technology equipment malfunctions, operational errors, and inaccuracies within software or data processing systems may also disrupt business operations or impact critical data. Market events also may trigger a volume of transactions that overloads current information technology and communication systems and processes, impacting the ability to conduct a Fund’s operations.

Cyber-attacks, disruptions, or failures may adversely affect a Fund and its shareholders or cause reputational damage and subject a Fund to regulatory fines, litigation costs, penalties or financial losses, reimbursement or other compensation costs, and/or additional compliance costs. For example, a Fund’s or its service providers’ assets or sensitive or confidential information may be misappropriated, data may be corrupted, and operations may be disrupted (e.g., cyber-attacks or operational failures may cause the release of private shareholder information or confidential Fund information, interfere with the processing of shareholder transactions, impact the ability to calculate a Fund’s NAV, and impede trading). In addition, cyber-attacks, disruptions, or failures involving a Fund counterparty could affect such counterparty’s ability to meet its obligations to the Fund, which may result in losses to the Fund and its shareholders. Similar types of operational and technology risks are also present for issuers of securities held by a Fund, which could have material adverse consequences for such issuers, and may cause the Fund’s investments to lose value. Furthermore, as a result of cyber-attacks, disruptions, or failures, an exchange or market may close or issue trading halts on specific securities or the entire market, which may result in a Fund being, among other things, unable to buy or sell certain securities or financial instruments or unable to accurately price its investments.

While a Fund and its service providers may establish business continuity and other plans and processes that seek to address the possibility of and fallout from cyberattacks, disruptions, or failures, there are inherent limitations in such plans and systems, including that they do not apply to third parties, such as Fund counterparties, issuers of securities held by a Fund, or other market participants, as well as the possibility that certain risks have not been identified or that unknown threats may emerge in the future and there is no assurance that such plans and processes will address the possibility of and fallout from cyber-attacks, disruptions, or failures. In addition, a Fund cannot directly control any cybersecurity plans and systems put in place by its service providers, Fund counterparties, issuers of securities held by the Fund, or other market participants.

LIBOR Transition Risk. The Fund may invest in securities or derivatives that are based on the London Interbank Offered Rate (LIBOR). LIBOR transition risk is the risk that the transition away from LIBOR to alternative interest rate benchmarks is not orderly, occurs over various time periods or has unintended consequences.

Trustees, Officers and Adviser. The Board of Trustees of the William Blair Funds (the “Trust”) has overall management responsibility. The duties of the trustees and officers of the Trust include overseeing the business affairs of the Trust, monitoring investment activities and practices and considering other matters concerning the Trust. The Statement of Additional Information has the names of and additional information about the trustees and officers of the Trust. Subject to the oversight of the Board of Trustees, William Blair Investment Management, LLC (the “Adviser” or “WBIM”), 150 North Riverside Plaza, Chicago, Illinois 60606, is responsible for providing investment advisory and management services to the Funds, including making decisions regarding Fund portfolio transactions, pursuant to a management agreement (the “Management Agreement”). The Statement of Additional Information includes information on brokerage commissions paid by the Funds in 2019, including amounts directed to third parties to pay for third party research. William Blair & Company, L.L.C. is the principal underwriter and distributor of the Trust and acts as agent of the Trust in the sale of its shares (the “Distributor” or “WBC”). WBIM and WBC are collectively referred to herein as “William Blair.”

William Blair was founded over 80 years ago by William McCormick Blair. As of December 31, 2019, William Blair had over 1,550 employees including approximately 180 partners. WBIM oversees the assets of the Trust, along with corporate pension plans, endowments and foundations. As of December 31, 2019, WBIM managed over $58 billion in equities, fixed income securities, derivatives and cash equivalents.

The Adviser firmly believes that clients are best served when portfolio managers are encouraged to draw on their experience and develop new ideas. This philosophy has helped build a hard-working, results-oriented team of 22 portfolio managers, supported by a team of analysts. The Adviser is registered as an investment adviser under the Investment Advisers Act of 1940.

The Fund’s contractual management fee is equal to the percentage of the Fund’s average daily net assets shown below:

Expense Waivers. The Adviser has entered into a contractual agreement with each Fund listed below to waive fees and/or reimburse expenses, if necessary, in order to limit the Fund’s operating expenses (excluding interest expenses, taxes, brokerage commissions, acquired fund fees and expenses, dividend and interest expenses on short sales, other investment-related costs and extraordinary expenses, such as litigation and other expenses not incurred in the ordinary course of the Fund’s business) for each class to the levels reflected in the table below

until April 30, 2021. The agreement terminates upon the earlier of April 30, 2021 or the termination of the Management Agreement.

With respect to the Small-Mid Cap Core Fund, the Adviser is entitled to recoupment of previously waived fees and reimbursed expenses for a period of three years subsequent to the Fund’s commencement of operations to the extent that such recoupment does not cause the annual Fund operating expenses (after the recoupment is taken into account) to exceed both (1) the expense limit in place when such amounts were waived or reimbursed and (2) the Fund’s current expense limitation.

Because of the expense limitation agreement, and for the Small-Mid Cap Core Fund the recoupment provision, each Fund may pay the Adviser less than the contractual management fee.

Board Considerations of Management Agreement. The Semi-Annual Report for the period ending June 30, 2020 will contain a discussion regarding the factors the Board of Trustees considered for the renewal of the Management Agreement for each Fund except the Small-Mid Cap Core Fund. The Annual Report for the period ending December 31, 2019 contains a discussion of the factors the Board of Trustees considered for the approval of the Management Agreement for the Small-Mid Cap Core Fund

Additional Information. The Trust enters into contractual arrangements with various parties, including, among others, each Fund’s investment adviser, custodian, transfer agent, accountants and distributor, who provide services to each Fund. Shareholders are not parties to, or intended (or “third-party”) beneficiaries of, any of those contractual arrangements, and those contractual arrangements are not intended to create in any individual shareholder or group of shareholders any right to enforce the terms of the contractual arrangements against the service providers or to seek any remedy under the contractual arrangements against the service providers, either directly or on behalf of the Trust.

This Prospectus provides information concerning the Trust and the Funds that you should consider in determining whether to purchase shares of a Fund. Each Fund may make changes to this information from time to time. Neither this Prospectus, the SAI or any document filed as an exhibit to the Trust’s registration statement, is intended to, nor does it, give rise to an agreement or contract between the Trust or any Fund and any

shareholder, or give rise to any contract or other rights in any individual shareholder, group of shareholders or other person other than any rights conferred explicitly by federal or state securities laws that may not be waived.

Portfolio Management. Additional information is provided below on each Fund’s portfolio manager(s) identified in the Summary section. The Statement of Additional Information provides additional information about the portfolio managers including the structure of their compensation, other accounts they manage and their ownership of securities in the Funds.

For each Fund that is managed by a portfolio management team, each member of the portfolio management team has equal responsibility for the Fund’s investment strategy, asset allocation, portfolio construction and security selection. All portfolio managers are supported by a team of research analysts.

Michael P. Balkin, a Partner of William Blair Investment Management, LLC, has co-managed the Small Cap Growth Fund from its inception in 1999 until 2005 and has co-managed the Fund since 2008. He returned to William Blair in 2008 after spending three years (2005-2008) as a partner with Magnetar Capital and as the Chief Investment Officer of Magnetar Investment Management. Prior to joining Magnetar in 2005, he spent fifteen years (1990-2005) with William Blair in various positions, including serving as a co-manager of the Small Cap Growth Fund from its inception in 1999 to 2005. Education: B.A., Northwestern University.

Daniel Crowe, a Partner of William Blair Investment Management, LLC, has co-managed the Mid Cap Growth Fund and the Small-Mid Cap Growth Fund since 2015 and the Small-Mid Cap Core Fund since its inception in 2019. He joined William Blair as a research analyst in 2011. Prior to joining William Blair, he was a midcap portfolio manager at Pyramis Global Advisors, and prior to that he was a portfolio manager and analyst at The Boston Company/Founders Asset Management. He began his career as a generalist analyst at Marsico Capital Management. He has the Chartered Financial Analyst designation and is a member of the CFA Institute and the CFA Society of Chicago. Education: B.S., Mechanical Engineering, University of Illinois at Urbana-Champaign.

Simon Fennell, a Partner of William Blair Investment Management, LLC, has co-managed the International Growth Fund since 2013, the Institutional International Growth Fund since 2013, the International Leaders Fund since 2013 and the International Small Cap Growth Fund since 2017 along with associated separate accounts and commingled fund portfolios. He joined William Blair in 2011 as a research analyst, also focusing on idea generation and strategy more broadly. Prior to joining William Blair, he was a Managing Director in the Equities division at Goldman Sachs in London and Boston, where he was responsible for institutional, equity research coverage for European and International stocks. Previously, he was in the Corporate Finance Group at Lehman Brothers in London and Hong Kong, working in the M&A and Debt Capital Markets Groups. Education: M.A., University of Edinburgh; M.B.A., Johnson Graduate School of Management, Cornell University.

Andrew G. Flynn, a Partner of William Blair Investment Management, LLC, has co-managed the International Small Cap Growth Fund since 2013 and the Global Leaders Fund since 2016 along with associated separate accounts and commingled fund portfolios. Mr. Flynn joined the International team in 2007 and conducted research across several sectors before becoming a portfolio manager. Prior to joining the International team, Mr. Flynn focused on domestic Consumer and Industrial companies at William Blair for two years. Before joining William Blair, Mr. Flynn was employed as a Senior Equity Analyst and Portfolio Manager at Northern Trust specializing in mid and small cap growth companies. Prior to that he worked as a Senior Equity Analyst at Scudder Kemper Investments and began his career at Fidelity Investments as a Research Assistant. He has the Chartered Financial Analyst designation and is a member of the CFA Institute and the CFA Society of Chicago. Education: B.A., Economics, University of Kansas; M.B.A., Finance emphasis, University of North Carolina at Chapel Hill.

David C. Fording, a Partner of William Blair Investment Management, LLC, has managed or co-managed the Growth Fund since 2006. He joined William Blair in November of 2005 as a co-portfolio manager of William Blair’s Institutional All Cap Growth strategy. He joined William Blair from TIAA-CREF Investment

Management, Inc. where he spent ten years, most recently as a co-portfolio manager of the TIAA-CREF Mid Cap Growth Fund Team (from 2003 to 2005). Previously, he was an equity analyst for TIAA-CREF responsible for covering media and entertainment stocks on a global basis. He was also a member of TIAA-CREF’s Large Cap Growth portfolio management team from 1997 to 1999. He has the Chartered Financial Analyst designation and is a member of the CFA Institute and the CFA Society of Chicago. In addition, he is a Fundamentals of Sustainability Accounting Credential holder. Education: B.A., Tufts University; M.B.A., Stern School of Business, New York University.

James S. Golan, a Partner with William Blair Investment Management, LLC, has co-managed the Large Cap Growth Fund since 2005. He joined William Blair in 2000 as a research analyst. In 2005, he joined the Institutional Large Cap Growth Team as a co-portfolio manager. Previously, he was a research analyst with Citigroup Global Asset Management and Scudder Kemper Investments. He has the Chartered Financial Analyst designation and is a member of the CFA Institute and the CFA Society of Chicago. Education: B.A., DePauw University; M.B.A., Northwestern University Kellogg Graduate School of Management.

James E. Jones, a Partner of William Blair Investment Management, LLC, has co-managed the Small-Mid Cap Growth Fund and the Mid Cap Growth Fund since 2019. He joined William Blair in 2010 as a research analyst focusing on U.S. small-cap industrials. From 2017 to 2019, he was a co-director of research for the U.S. Growth Equity team at William Blair. Before joining William Blair in 2010, he was an investment analyst at Federated Investors. He has the Chartered Financial Analyst designation and is a member of the CFA Institute and the CFA Society of Chicago. Education: B.S., Accounting, Miami University; M.B.A., the University of North Carolina.

Chad M. Kilmer, a Partner with William Blair Investment Management, LLC, has co-managed the Small Cap Value Fund since 2006 and the Small-Mid Cap Value Fund since its inception in 2011. He joined William Blair in 2006. Prior to joining William Blair, he was employed by US Bancorp Asset Management from 2004 to 2006 in various capacities, including as the manager of the First American Funds Small Cap Value Fund, managing institutional separate portfolios, and buy-side research. Previously, he was an investment analyst at Gabelli Woodland Partners, a subsidiary of Gabelli Asset Management. He has the Chartered Financial Analyst and Certified Public Accountant designations and is a member of the CFA Institute and the CFA Society of Chicago. Education: B.S.B., University of Minnesota; M.B.A., Yale University School of Management.

Robert C. Lanphier IV, a Partner of William Blair Investment Management, LLC, has co-managed the Mid Cap Growth Fund since its inception in 2006, the Small-Mid Cap Growth Fund since its inception in 2003 and the Small-Mid Cap Core Fund since its inception in 2019. He began with William Blair in December 1987 as an associate in the Institutional Sales Department. In January 1996, he became a portfolio manager. Previously, he was with Emerson Electric Corporation in a variety of corporate planning and international consulting activities from 1982 to 1987. Effective September 30, 2020, Mr. Lanphier will retire as a portfolio manager. Education: B.S., Purdue University; M.B.A., Northwestern University Kellogg Graduate School of Management.

Mark T. Leslie, a Partner of William Blair Investment Management, LLC, has co-managed the Small Cap Value Fund since 2005 and the Small-Mid Cap Value Fund since its inception in 2011. He has been with William Blair since 2005. Prior to joining William Blair, he was employed by US Bancorp Asset Management from 1997 to 2005 in various capacities, including the manager of the First American Funds Small Cap Value Fund and First American Funds Mid Cap Value Fund and managing institutional portfolios. He began his career in the financial industry in 1990 and started portfolio management in 1998. Previously, he was a research analyst at Dain Bosworth and an investment associate at Investment Advisers Inc. He has the Chartered Financial Analyst designation and is a member of the CFA Institute and the CFA Society of Chicago. Education: B.S., Business Administration, University of New Hampshire.

Kathleen M. Lynch, an Associate of William Blair Investment Management, LLC, has co-managed the Low Duration Fund since 2020. She has been with William Blair since 1999 when she started as a tax-exempt trader and later became a portfolio manager of municipal securities for the fixed-income team. In 2008, Ms. Lynch

became the lead portfolio manager for William Blair’s money market fund until its liquidation in 2015. Prior to joining William Blair, she was a middle markets fixed income associate at Citigroup where she was responsible for facilitating trades in taxable and tax-exempt fixed income securities. She has the Chartered Financial Analyst designation and is a member of the CFA Institute and the CFA Society of Chicago. Education: B.S. B.A. in Finance, University of Dayton.

Kenneth J. McAtamney, a Partner of William Blair Investment Management, LLC, has co-managed the Global Leaders Fund since 2008, the International Leaders Fund since its inception in 2012, the International Growth Fund since 2017 and the Institutional International Growth Fund since 2017 along with associated separate account and commingled fund portfolios. He joined William Blair in 2005 as an international stock analyst. From 1997 to 2005, he was with Goldman Sachs in various capacities, including as a Vice President representing both International and Domestic Equities. Education: B.A., Finance, Michigan State University; M.B.A., Indiana University.

Todd M. McClone, a Partner of William Blair Investment Management, LLC, has co-managed the Emerging Markets Growth Fund since its inception in 2005, the Emerging Markets Leaders Fund since 2008 and the Emerging Markets Small Cap Growth Fund since its inception in 2011 along with associated separate account and commingled fund portfolios. He has been with William Blair since 2000. From 1993 through 2000, he was a senior research analyst specializing in international equity for Strong Capital Management. Prior to joining Strong Capital Management, he was a Corporate Finance Research Analyst with Piper Jaffray. At Piper Jaffray, he worked with the corporate banking financials team on a variety of transactions including initial public offerings, mergers and acquisitions and subordinated debt offerings, and issued fairness opinions and conducted private company valuations. He has the Chartered Financial Analyst designation and is a member of the CFA Institute. Education: B.B.A. and B.A., University of Wisconsin-Madison.

David S. Mitchell, a Partner of William Blair Investment Management, LLC, has managed or co-managed the Small Cap Value Fund since its inception in 1996 and has co-managed the Small-Mid Cap Value Fund since its inception in 2011. He joined William Blair in 1996 as a small cap value portfolio manager. Prior to joining William Blair, he was a Partner in the U.S. Equity Group at Brinson Partners, Inc. and a member of the Post-Venture Portfolio management team until 1996. Previously, he was co-manager of Thomas Paine Investors, LP, a private fund that invested in small cap stocks, after working as a Senior Equity Analyst on NBD’s Woodward Opportunity Fund. He was an equity analyst and portfolio manager at Connecticut National Bank and, prior to graduate studies, an equity trader and money market portfolio manager. For more than a decade, he served as a director at Reading in Motion, which partners with teachers to improve urban children’s language arts and learning skills through the arts. He is also a general trustee of Knox College. He has the Chartered Financial Analyst designation and is a member of the CFA Institute and the CFA Society of Chicago. Education: B.A., Knox College; M.B.A., Northwestern University Kellogg Graduate School of Management.

John C. Murphy, a Partner of William Blair Investment Management, LLC, has co-managed the Emerging Markets Leaders Fund since 2016, along with associated separate account portfolios. Mr. Murphy was previously the Global Consumer sector team leader, and was responsible for conducting research on large-mid cap non-U.S. Consumer stocks. Mr. Murphy was a Research Analyst within William Blair’s sell-side Research Department focusing on e-commerce and hardline retailers prior to joining the International team. Prior to joining William Blair in 2005, Mr. Murphy worked at Credit Suisse First Boston for nearly six years as an equity research analyst covering a broad range of retail companies. Before working at Credit Suisse First Boston, Mr. Murphy worked as an equity research analyst at Lehman Brothers and as an equity research associate at Salomon Brothers. Prior to sell-side research, he worked as a financial analyst for General Electric Capital, having graduated from GE’s Financial Management Program. He has the Chartered Financial Analyst designation and is a member of the CFA Institute and the CFA Society of Chicago. Education: B.A., Villanova University, magna cum laude.

Casey Preyss, a Partner of William Blair Investment Management, LLC, has co-managed the Emerging Markets Growth Fund since 2015 and the Emerging Markets Small Cap Growth Fund since 2016 along with associated

separate account and commingled fund portfolios. Having joined William Blair in 2000, Mr. Preyss was previously a research analyst covering the Industrials, IT and Resources sectors and also served as the Global Industrials Sector Team Leader. Prior to his research responsibilities, Mr. Preyss was a Quantitative Analyst with the team. Prior to joining William Blair, Mr. Preyss was with Thomas White International as an International Equity Research Sales Associate. Education: B.S. B.A., The Ohio State University; M.B.A., University of Chicago Booth School of Business.

David P. Ricci, a Partner of William Blair Investment Management, LLC, has co-managed the Large Cap Growth Fund since 2011. He has been with William Blair since February 1994 when he started as a research analyst for the Consumer/Retail sell-side research effort at William Blair. He was made group head in June 2001. Previously, he was with Procter & Gamble, Melville, and spent 2 1/2 years as a strategy consultant at Bain & Company. He has the Chartered Financial Analyst designation and is a member of the CFA Institute and the CFA Society of Chicago. Education: Sc.B., Brown University, magna cum laude; M.B.A., Harvard Business School.

Ward D. Sexton, a Partner of William Blair Investment Management, LLC, has co-managed the Small Cap Growth Fund since 2016 and the Small-Mid Cap Core Fund since its inception in 2019. In 2001, he joined the Fund’s investment team as a research analyst and covered Resources Financials and Consumer companies at various points during his time as an analyst. He joined William Blair in 1999 and worked in the firm’s corporate finance group for two years. He has the Chartered Financial Analyst designation and is a member of the CFA Institute and the CFA Society of Chicago. Education: B.S., Finance with honors, University of Illinois Urbana-Champaign; M.B.A., high honors, University of Chicago Booth School of Business.

Paul J. Sularz, an Associate of William Blair Investment Management, LLC, has co-managed the Bond Fund since 2010 and the Low Duration Fund since its inception in 2009. Mr. Sularz joined William Blair in July 2006 as a fixed income portfolio manager. Prior to joining William Blair, he was a Vice President at J.P. Morgan Securities, Inc. from 2004 to 2006, where he was responsible for trading specified pool agency mortgage-backed pass-through securities for the firm’s primary broker/dealer in New York City. Prior to this, he was a Director at Banc One Capital Markets, Inc. within the Asset-Backed and Mortgage-Backed Securities Group from 1995- 2004, managing the firm’s mortgage-backed securities trading desk in Chicago. His investment career began in 1990 at Kemper Asset Management Company, where he was an Assistant Portfolio Manager within the fixed income Institutional Asset Management Division. Education: B.A. in Economics, University of Illinois at Urbana-Champaign; M.B.A., concentrations in Finance, Econometrics and Statistics, University of Chicago Booth Graduate School of Business.

Ruta Ziverte, an Associate of William Blair Investment Management, LLC, has co-managed the Bond Fund and managed the Income Fund since 2020. Ms. Ziverte oversees the fixed income team at William Blair. She joined William Blair in 2019. Prior to joining William Blair, she worked at Oppenheimer Funds from 2015 to 2019, where she was the portfolio manager for the Global High Yield Fund and co-portfolio manager for the Global Strategic Income Fund. She also led a team of fixed-income credit analysts. Prior to that, she was employed by GE Asset Management in various capacities, including as executive managing director and high-yield portfolio manager, and as a team leader and senior analyst, co-managing a leveraged finance research team, and was responsible for developing and implementing the firm’s credit processes and procedures. Education: B.S., Finance, University of Latvia; M.B.A., Rensselaer Polytechnic Institute.

The historical performance data shown below represents the actual performance of a composite of all accounts previously managed by the Adviser with substantially similar objectives, policies, strategies and risks as the Small-Mid Cap Core Fund since the composite’s inception on June 1, 2017.

The performance shown is not that of the Small-Mid Cap Core Fund and is provided solely to illustrate the prior performance of the Adviser in a substantially similar strategy and does not indicate the future performance of the

Small-Mid Cap Core Fund. Past performance does not guarantee future results. Results may differ because of, among other things, differences in brokerage commissions, account expenses including management fees, the size of positions taken in relation to account size, diversification of the account, timing of purchases and sales and availability of cash for new investment.

Returns include all dividends, interest, realized and unrealized gains and losses. The performance information is presented net and gross of the Fund’s “Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement” as included in the “Annual Fund Operating Expenses” table on p. 16 of this prospectus. Account returns are calculated daily using a time-weighted return methodology with adjustments for cash flows. Monthly account performance is calculated by linking the daily returns. Monthly composite returns are calculated by asset weighting individual account monthly returns using beginning-of-period values. This method of calculation differs from the SEC’s formula for a registered investment company to calculate average annual total return.

The performance shown below is not that of a registered investment company under the Investment Company Act of 1940 (the “1940 Act”) and, as a result, has not been subject to the restrictions and investment limitations imposed by the 1940 Act and the Internal Revenue Code of 1986, as amended (the “Code”) (including, for example, diversification and liquidity requirements and restrictions on transactions with affiliates). The performance may have been adversely affected had it been subject to regulation as an investment company under the 1940 Act and the Code.

Custodian. The Custodian for the Funds is State Street Bank and Trust Company, State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111. The Custodian is responsible for custody of portfolio securities, fund accounting and the calculation of each Fund’s net asset value.

Transfer Agent and Dividend Paying Agent. The Transfer Agent and Dividend Paying Agent is DST Asset Manager Solutions, Inc. (“DST”), 2000 Crown Colony Drive, Quincy, Massachusetts 02169-0953.

Class N shares are offered to investors who acquire the shares directly through the Distributor or through those financial intermediaries with whom the Distributor has entered into written agreements specifically authorizing them to sell Class N shares. Investors may hold Class N shares through a taxable account or through certain tax-advantaged accounts.

Minimum Investments. The minimum initial investment for an account generally is $2,500. The minimum subsequent investment generally is $1,000. William Blair may make exceptions to these requirements, which are discussed below.

Class I shares are offered to investors who acquire the shares directly through the Distributor or through those financial intermediaries with whom the Distributor has entered into written agreements specifically authorizing them to sell Class I shares.

Class I shares are available for purchase by the following categories of investors who meet the minimum investment requirements (except as noted):

To the extent a shareholder or group of shareholders (either directly or through an intermediary) are not listed in the above categories but they held Class I shares of a Fund prior to May 1, 2019, such investors are entitled to continue to invest in Class I shares of that Fund.

Minimum Investments. The minimum initial investment for an account generally is $500,000 (or any lesser amount if, in William Blair’s opinion, the investor has adequate intent and availability of funds to reach a future level of investment of $500,000). There is no minimum for subsequent purchases.

William Blair may make certain additional exceptions to these requirements, which are discussed below. The Funds will consider requests by holders of Class N shares to convert such shares to Class I shares on a case by case basis, provided eligibility requirements and relevant minimums are met.

Class R6 shares are offered to investors who acquire the shares directly through the Distributor or through those financial intermediaries with whom the Distributor has entered into written agreements specifically authorizing them to sell Class R6 shares.

Class R6 shares are offered to the following investors, provided that neither these investors nor their intermediaries require a Fund to make any type of servicing or administrative payments with respect to Class R6 shares:

Class R6 shares are not available to retail taxable or tax-advantaged accounts seeking to invest directly in the Funds outside of an omnibus account maintained by an intermediary, except as noted above. To the extent a shareholder or group of shareholders (either directly or through an intermediary) are not listed in the above categories but they held Institutional Class shares of a Fund prior to May 1, 2019, such investors are entitled to continue to invest in Class R6 shares of that Fund. The Funds will consider requests by holders of Class I shares to convert such shares to Class R6 shares on a case by case basis, provided eligibility requirements and relevant minimums are met.

Minimum Investments. The minimum initial investment for an account is $1 million (or any lesser amount if, in William Blair’s opinion, the investor has adequate intent and availability of funds to reach a future level of investment of $1 million). There is no minimum for subsequent purchases.

William Blair’s partners and employees, the Board members of the Trust and their family members will not be subject to the minimum investment requirement. Tax-exempt retirement plans (Profit Sharing, 401(k), Money Purchase Pension and Defined Benefit Plans) of William Blair and its affiliates and rollover accounts from those plans will also be exempt from the minimum investment requirement. William Blair may make certain additional exceptions to these requirements, which are discussed below.

Share Class Minimum Maintenance. If an account’s balance falls below the minimum initial investment amount for that share class due to account redemptions (and not due to market depreciation), the Funds reserve the right to convert or redeem shares held by the account in the following manner:

The applicable shareholder or intermediary will be notified prior to any such redemption or conversion and will be allowed 60 days to make additional investments and bring the account into compliance with the applicable investment minimum before any conversion or redemption occurs. Any conversion will occur at the relative net asset value of the two applicable share classes at the time of conversion and the account value will not change as a result of the conversion, although the number of shares held may change.

Where a retirement plan or other financial intermediary holds Class I or Class R6 shares on behalf of its participants or clients, shares held by such participants or clients will be converted to Class N shares as described above when a participant or client rolls over its accounts with the retirement plan or financial intermediary into an individual retirement account and such participant or client is not otherwise eligible to purchase Class I or Class R6 shares.

A conversion between share classes of the same Fund is generally not a taxable event. Please consult your tax advisor for an assessment of the tax implications of any conversion.

ADDITIONAL INFORMATION AND EXCEPTIONS TO ELIGIBILITY AND MINIMUM INVESTMENT REQUIREMENTS FOR CLASS N, CLASS I AND CLASS R6 SHARES

The Distributor may accept investments that are less than the minimums set forth above under a group payroll deduction or similar plan. Investors investing through certain tax-qualified retirement plans and wrap fee programs may be subject to different, lower or no minimums. For omnibus accounts that meet the minimum investment requirement, the Trust does not impose any minimum investment amounts for sub-accounts, although the firm holding the omnibus account may impose its own minimum investment requirements. The Distributor may, in its discretion, waive or reduce investment minimums in other circumstances.

The Trust does not impose any sales charges in connection with purchases of Class N, Class I or Class R6 shares, although financial intermediaries and other institutions may charge their clients a fee in connection with purchases for the accounts of their clients.

The Distributor may, in its sole discretion, reject any purchase order from the shareholder and/or intermediary involved.

Distribution Agreement. The Trust has adopted a plan under Rule 12b-1 of the Investment Company Act of 1940, as amended (the “1940 Act”), that applies only to Class N shares that provides for a fee at the annual rate of 0.25% of each Fund’s average daily net assets attributable to Class N shares (0.15% for the Bond Fund, the Income Fund and the Low Duration Fund) for distribution and other services provided to shareholders of

Class N. Because 12b-1 fees are paid out of Fund assets on an ongoing basis, they will, over time, increase the cost of investment in Class N shares and may cost more than other types of sales charges. As a result, long-term shareholders may pay more than the economic equivalent of the maximum initial sales charge permitted by FINRA.

Class N and Class I shares of the Funds may reimburse William Blair for fees paid on a Fund’s behalf to intermediaries such as banks, broker-dealers, financial advisers or other financial institutions for sub-administration, sub-transfer agency and other services provided to shareholders whose shares are held of record in omnibus, other group accounts, retirement plans or accounts traded through registered securities clearing agents. These fees may be based on the number of subaccounts serviced or based on average net assets held in the Funds for Class N and Class I shares.

William Blair, out of its own resources and without additional cost to the Funds or their shareholders, provides additional cash payments to certain intermediaries (which may be referred to as revenue sharing). Such payments to intermediaries are in addition to distribution fees or fees for sub-administration, sub-transfer agency or other services paid or payable by Class N or Class I shares of the Funds. William Blair may pay firms for administrative, sub-accounting, or shareholder processing services and/or for providing Class N, Class I or Class R6 shares of the Funds with “shelf space” or access to a third party platform, inclusion of Class N, Class I or Class R6 shares of the Funds on preferred or recommended sales lists, mutual fund “supermarket” platforms and other sales programs, allowing William Blair access to an intermediary’s conferences and meetings and other forms of marketing support. The level of payments made may be a fixed fee or based on one or more of the following factors: current assets, number of accounts and/or number of transactions for Class N, Class I or Class R6 shares attributable to the intermediary or fund type or other measure agreed to by William Blair and the intermediary. The amount of payments is different for different intermediaries.

The Distributor currently makes payments to intermediaries in amounts that generally range from 0.01% to 0.15% of the assets of the Funds’ shares serviced and maintained by the intermediary. These amounts are subject to change. Receipt of, or the prospect of receiving, this compensation may influence the intermediary’s recommendation of the Funds or availability of the Funds through the intermediary. Further information on payments to third parties is included in the Statement of Additional Information.

INTERNATIONAL GROWTH FUND, INSTITUTIONAL INTERNATIONAL GROWTH FUND, INTERNATIONAL SMALL CAP GROWTH FUND AND EMERGING MARKETS SMALL CAP GROWTH FUND

The International Growth Fund, the Institutional International Growth Fund, the International Small Cap Growth Fund and the Emerging Markets Small Cap Growth Fund are closed to investors, except as noted below. Unless you fit into one of the investor categories described below, you may not invest in the Funds.

You may purchase Fund shares through your existing Fund account and reinvest dividends and capital gains in the Fund if you are:

You may open a new Fund account or purchase Fund shares through an existing Fund account if you are:

Except as otherwise noted, these restrictions apply to investments made directly with William Blair and investments made through financial institutions and/or intermediaries. Once an account is closed, additional investments will not be accepted unless you are one of the investors listed above. Exchanges of Class N, Class I and Class R6 shares into the Funds from other Funds are not permitted unless the exchange is being made into an existing Fund account. Investors may be required to demonstrate eligibility to purchase shares of the Funds before an investment is accepted. Management reserves the right to (i) make additional exceptions that, in its judgment, do not adversely affect its ability to manage the Funds, (ii) reject any investment or refuse any exception, including those detailed above, that it believes will adversely affect its ability to manage the Funds, and (iii) close and re-open the Funds to new or existing shareholders at any time.

The information below relating to buying, selling and exchanging shares of the Funds applies if you are transacting directly with the Funds. Shares of the Funds are also available through certain financial intermediaries, such as a bank or a broker-dealer (each, an “intermediary”). If you are investing through an intermediary, you are not placing your orders directly with the Funds, and you must follow the intermediary’s transaction procedures. Your intermediary may impose different or additional conditions than the Funds on purchases, redemptions and exchanges of Fund shares. These differences may include different minimum initial (and subsequent) investment amounts, exchange policies, fund choices, cut-off times for investment and other trading restrictions. Your intermediary also may impose charges for its services in addition to the fees charged by the Funds. You should consult with your intermediary directly for information regarding its conditions and fees for buying, selling or exchanging shares of the Funds. The Funds are not responsible for the failure of your intermediary to carry out its responsibilities.

Purchase Price. All Funds are sold at their public offering price, which is the net asset value per share that is next computed after receipt of your order in proper form by the Distributor, the Transfer Agent or a designated agent thereof. (For more information, see “Determination of Net Asset Value.”) If you fail to pay for your order, you will be liable for any loss to a Fund and, if you are a current shareholder, the Fund may redeem some or all of your shares to cover such loss.

Note: All purchases made by check should be in U.S. dollars and made payable to William Blair Funds, or in the case of a retirement account, the custodian or trustee of such account. Third party checks generally will not be accepted. When purchases are made by check or periodic account investment, the Funds may delay sending redemption proceeds until they determine that collected funds have been received for the purchase of such shares, which may be up to 15 calendar days.

Purchase in Kind. You may, subject to the approval of the Funds, purchase shares of the Funds with securities that are eligible for purchase by the Funds (consistent with the Funds’ investment process, goal and philosophy) and that have values that are readily ascertainable in accordance with the Funds’ valuation policies. Call the Funds at 1-800-742-7272 if you would like to purchase shares of the Funds with other securities. Such purchases may result in the recognition of gain or loss for federal income tax purposes on the securities transferred to the Funds.

Right to Reject Your Purchase Order. The Trust is required to obtain, verify and record certain information regarding the identity of shareholders. When opening a new account, the Trust will ask for your name, address, taxpayer identification number, date of birth and other information that identifies you. You may also be asked to show identifying documents. Applications without this information may not be accepted and orders may not be processed. The Trust reserves the right to place limits on transactions in any account until the identity of the investor is verified; refuse an investment in the Funds or involuntarily redeem an investor’s shares and close an account in the event that an investor’s identity is not verified; or suspend the payment of withdrawal proceeds if it is deemed necessary to comply with anti-money laundering regulations. The Trust and its agents will not be responsible for any loss resulting from an investor’s delay in providing all required identifying information or from closing an account and redeeming an investor’s shares when an investor’s identity cannot be verified.

The Trust is required to comply with various federal anti-money laundering laws and regulations. As a result, the Trust may be required to “freeze” a shareholder account if the shareholder appears to be involved in suspicious activity or if account information matches information on government lists of known terrorists or other suspicious persons, or the Trust may be required to transfer the account or account proceeds to a government agency. The Trust may also be required to reject a purchase payment, block an investor’s account and consequently refuse to implement requests for transfers, withdrawals, surrenders or death benefits.

Short-Term and Excessive Trading. The Funds are designed for long-term investors. All Funds discourage and do not accommodate short-term or excessive trading. Such trading may present risks to other shareholders in the Funds, including disruption of portfolio investment strategies, with potential resulting harm to performance, and increased trading costs or Fund expenses. Thus, such trading may negatively impact the Funds’ net asset value and result in dilution to long-term shareholders. Short-term and excessive trading in Fund shares can also negatively impact the Funds’ long-term performance by requiring the Funds to maintain more assets in cash or to liquidate holdings at a disadvantageous time. These risks may be more pronounced for the Funds investing in securities that are susceptible to pricing arbitrage (e.g., international securities, emerging markets securities and small cap securities).

In an effort to protect long-term shareholders, the Board of Trustees has adopted policies and procedures that seek to deter short-term and excessive trading and to detect such trading activity at levels that may be detrimental to the Funds. The Funds reserve the right to reject or restrict any purchase order (including exchanges) from any investor for any reason, including excessive, short-term or other abusive trading practices that may disrupt portfolio management strategies and harm Fund performance. The Funds also reserve the right to delay delivery of redemption proceeds up to seven days or to honor certain redemptions with securities, rather than cash.

In making the determination to exercise these rights, the Funds may consider an investor’s trading history in the Funds and accounts under common ownership or control. The Funds seek to employ reasonable measures to detect short-term and excessive trading at levels that may be detrimental to the Funds. Accordingly, the Adviser uses certain materiality and volume thresholds to detect short-term or excessive trading, but otherwise seeks to apply the policies uniformly to all shareholders, as described in more detail below.

engage in short-term or excessive trading may use a variety of strategies to avoid detection and, despite the efforts of the Funds and their agents to prevent short-term or excessive trading, there is no guarantee that the Funds or their agents will be able to identify such shareholders or curtail their trading practices. Also, the ability of the Funds and their agents to detect and curtail short-term and excessive trading practices may be limited by operational systems and technological limitations. In addition, the Funds receive purchase, exchange and redemption orders through financial intermediaries and cannot always know or reasonably detect short-term or excessive trading that may be facilitated by these intermediaries or by the use of omnibus account arrangements.

Under agreements that the Funds have entered into with intermediaries, the Funds may request transaction information from intermediaries at any time to determine whether there has been short-term trading by the intermediaries’ customers. The Funds will request that the intermediary provide individual account level detail (or participant level detail in the case of retirement plans) to the Funds at their request. If short-term trading is detected at the individual account or participant level, the Funds will request that the intermediary a) continue to monitor the individual or participant, b) issue the individual or participant a warning, or c) ban the individual or participant from making further purchases of Fund shares. An intermediary may apply its own short-term trading policies and procedures, which may be more or less restrictive than the Funds’ policies and procedures. There is no assurance that the Funds’ policies will be effective in limiting and deterring short-term and excessive trading in all circumstances.

Opening an Account—Class N shares and Class I shares. To open a new account for Class N shares or Class I shares of the Funds by mail, make out a check for the amount of your investment, payable to “William Blair Funds.” Complete the account application included with this Prospectus and mail the completed application and the check to the Transfer Agent, DST Asset Manager Solutions, Inc., P.O. Box 219137, Kansas City, Missouri 64121-9137.

Adding to an Account—Class N shares and Class I shares. To purchase additional Class N shares or Class I shares, make out a check for the amount of your investment, payable to “William Blair Funds” and mail the check, together with a letter that specifies the Fund name, the account number and the name(s) in which the account is registered, to DST Asset Manager Solutions, Inc., P.O. Box 219137, Kansas City, Missouri 64121-9137.

Opening or Adding to an Account—Class R6 shares. Opening a new account or adding to an account for Class R6 shares may only be done by wire. See “By Wire” below.

Opening an Account—Class N shares and Class I shares. First, call DST at 1-800-635-2886 (in Massachusetts, 1-800-635-2840) for an account number. Then instruct your bank to wire federal funds to:

Include the name of the Fund in which you are investing, your assigned account number and the name(s) in which the account is registered. Finally, complete the account application, indicate the account number assigned to you by DST and mail it to William Blair Funds, 150 North Riverside Plaza, Chicago, Illinois 60606.

Adding to an Account—Class N shares and Class I shares. To add to your account by wire, instruct your bank to wire federal funds to:

In your request, specify the name of the Fund in which you are investing, your account number, and the name(s) in which the account is registered. To add to an existing account by wire transfer of funds, you must have selected this option on your account application.

Opening or Adding to an Account—Class R6 shares. First, call the Distributor at 1-800-742-7272 for an account number. Then instruct your bank to wire federal funds to:

Include the name of the Fund in which you are investing, your assigned account number and the name(s) in which the account is registered. Finally, complete the account application, indicate the account number assigned to you by the Distributor and mail it to the Distributor, William Blair & Company, L.L.C., 150 North Riverside Plaza, Chicago, Illinois 60606.

Adding to an Account. Call DST at 1-800-635-2886 (in Massachusetts, 1-800-635-2840). You may then pay for your new shares by wire or by mail, except for Class R6 shares which may only be paid for by wire. To add to an existing account by telephone, you must have selected this option on your account application.

You can arrange to take money out of your account by selling (“redeeming”) some or all of your shares. You may give instructions to redeem your shares by mail, by wire or by telephone, as described below.

To redeem Class N shares, Class I shares or Class R6 shares by mail, send a written redemption request signed by all account owners to DST Asset Manager Solutions, Inc., P.O. Box 219137, Kansas City, Missouri 64121-9137.

To redeem some or all of your shares by wire you may contact DST by mail or telephone, as explained herein. To redeem by wire, you must have elected this option on your account application and attached to the application, for Class N shares and Class I shares, a voided, unsigned check or deposit slip for your bank account, and for Class R6 shares, a corporate resolution authorizing those able to act on your behalf.

To redeem shares by telephone, you must have elected this option on your account application. Contact DST at 1-800-635-2886 (in Massachusetts, 1-800-635-2840).

Note: Telephone redemption requests should NOT be directed to the Trust or to the Distributor.

Signature Guarantees. A signature guarantee may be required to redeem Class N shares and Class I shares in certain instances. A signature guarantee is not required for redemptions of Class R6 shares. Signature guarantees must be obtained from a bank that is a member of the FDIC, from a brokerage firm that is a member of FINRA or an exchange, or from an eligible guarantor who is a member of, or a participant in, a signature guarantee program. Your redemption request with respect to Class N shares or Class I shares must include a signature guarantee if any of the following situations apply:

Signature guarantees, if required, must appear on the written redemption request and on any endorsed stock certificate or stock power.

Redemption Price. The redemption price is the net asset value next calculated after receipt of your redemption request in proper order by the Distributor, Transfer Agent or a designated agent thereof. The redemption price that you receive for your shares may be more or less than the amount that you originally paid for them.

Payment for Redeemed Shares. Payment normally will be mailed to you at the address of record for your account by the third business day after receipt by DST of a redemption request and any other required documentation and after any checks in payment for your shares have cleared.

Under normal conditions, each Fund typically expects to meet redemption requests through the use of the Fund’s holdings of cash or cash equivalents or by selling other Fund assets. A redemption in kind may be used as discussed below.

Delayed Proceeds. The Trust reserves the right to delay delivery of your redemption proceeds—up to seven days—or to honor certain redemptions with securities, rather than cash, as described in the next section.

Redemptions In Kind. The Trust reserves the right to make redemption payments in whole or in part in securities or other financial assets, valued for this purpose as they are valued in computing the net asset value for the Funds’ shares. In making a redemption payment “in kind,” a Fund will typically distribute a pro rata portion of all securities or other financial assets, subject to certain exclusions approved by the Board of Trustees. Shareholders will receive cash for the portion of excluded securities and a Fund’s holdings of cash and receivables.

Notwithstanding the above, each Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1.00% of the net asset value of the Fund during any 90-day period for any one shareholder of record.

Automatic Redemptions. The Trust reserves the right to redeem your shares in any account that, following a redemption, is below a specified minimum amount. Currently, the minimum for Class N shares is $2,500 per account for regular accounts and IRAs, for Class I shares is $500,000 per account for regular accounts and IRAs, and for Class R6 shares is $1 million, unless the reduction in value is due solely to market depreciation. Before the redemption is processed, you will be notified that the value of your account has fallen below the minimum and allowed to make an additional investment.

Subject to the following limitations, you may exchange Class N, Class I or Class R6 shares of a Fund for the same class of shares of another William Blair Fund at their relative net asset values so long as the shares to be acquired are available for sale in your state of residence and the other William Blair Fund is open to new investors. Shareholders who purchase Class I shares of the Emerging Markets Leaders Fund solely because they have a brokerage account with William Blair & Company, L.L.C. and held Class I shares of the Fund on May 1, 2010 may only exchange their Class I shares of the Emerging Markets Leaders Fund for Class N shares of another Fund. Exchanges into a closed Fund are precluded unless the shareholder already has an open account in that Fund. Exchanges will be effected by redeeming your shares and purchasing shares of the other William Blair Fund(s) requested. Shares of a Fund with a value in excess of $1 million acquired by exchange from another Fund may not be exchanged thereafter until they have been owned for 15 days (the “15 Day Hold Policy”). Each Fund reserves the right to reject any exchange order for any reason, including excessive, short-term (market-timing) or other abusive trading practices that may disrupt portfolio management. Exchanges will result in the recognition for federal income tax purposes of gain or loss on the shares exchanged. You should obtain and carefully read the prospectus of the William Blair Fund(s) you want to exchange into prior to making an exchange. You may obtain a prospectus by calling 1-800-635-2886 or by going to the Trust’s website at williamblairfunds.com.

The Fund will consider requests by holders of Class N shares to convert such shares to Class I shares on a case by case basis, provided eligibility requirements and relevant minimums are met. Class I shares of a Fund may be exchanged for Class R6 shares of the Fund provided that your account meets the eligibility requirements for Class R6 shares and you meet the Class R6 investment minimums discussed above.

You may request an exchange of your shares by writing a letter that specifies the Fund name, the account number and the name(s) in which the account is registered, to William Blair Funds, Attention: Exchange Department, P.O. Box 219137, Kansas City, Missouri 64121-9137.

You may also exchange your shares by telephone by completing the appropriate section on your account application. Once your telephone authorization is on file, DST will honor your requests to exchange shares by telephone at 1-800-635-2886 (in Massachusetts, 1-800-635-2840).

Neither the Trust nor DST will be liable for any loss, expense or cost arising out of any telephone request pursuant to the telephone exchange privilege, including any fraudulent or unauthorized request, and you will bear the risk of loss, so long as the Trust or DST reasonably believes, based upon reasonable verification procedures, that the telephonic instructions are genuine. The verification procedures include (1) recording instructions,

(2) requiring certain identifying information before acting upon instructions and (3) sending written confirmations.

Income Dividends. The Funds may earn dividends from stocks and interest from bond, money market and other investments, as well as net short-term capital gains from sales of securities, all of which are passed through to shareholders as income dividends as long as expenses do not exceed income.

Capital Gain Distributions. The Funds may realize capital gains whenever they sell securities for a higher price than they paid for them, which then will generally be passed through to shareholders as capital gain distributions to the extent that a Fund’s net long-term capital gains exceed the sum of its net short-term capital losses for such year and any capital loss carryovers available from prior years.

As a shareholder, you are entitled to your portion of a Fund’s net income and gains on its investments. Each Fund passes its earnings along to you as dividends and distributions. Each Fund’s policy is to distribute substantially all net investment income, if any, and all realized net capital gain, if any. All distributions of income and capital gain and any return of capital have the effect of immediately thereafter decreasing net asset value per share. Income dividends and capital gain distributions will be automatically reinvested in additional shares at net asset value on the reinvestment date, unless you specifically request otherwise (see “Shareholder Services and Account Policies—Dividend Options”). Cash payments are made by the Dividend Paying Agent shortly following the reinvestment date.

The Funds may vary these dividend practices at any time. Income dividends and any capital gain distributions made by the Funds will vary from year to year. Dividends and distributions may be subject to withholding, as required by the Internal Revenue Service (the “IRS”) (see “Your Account—Federal Income Taxes”).

As with any investment, you should consider how your investment in a Fund will be taxed. If your account is not a tax-advantaged account, the federal income tax implications of your investment in a Fund include the following:

Taxes on Distributions. Each Fund’s distributions from current and accumulated earnings and profits are subject to federal income tax and may also be subject to state or local taxes. Distributions may be taxable at

different tax rates depending upon the type of security and the length of time the Fund holds the security generating the income or gain that is distributed. Your distributions are generally taxable when they are paid, whether you take them in cash or reinvest them in additional shares. However, dividends declared in October, November or December to shareholders of record as of a date in one of those months and paid before the following February 1 are treated as having been paid on December 31 of the calendar year declared for federal income tax purposes. After the close of each calendar year, the Funds will inform you of the amount and nature of distributions paid.

Under the federal income tax laws, net investment income, including interest and dividends (other than “qualified dividend income”), and net short-term capital gains are taxed as ordinary income. Distributions of qualified dividend income will generally be taxed to individuals and other non-corporate shareholders at rates applicable to long-term capital gains, provided the Fund and the shareholder each satisfy certain holding period and other requirements. Net capital gain distributions are taxed at long-term capital gain rates regardless of how long you have held your shares. It is anticipated that a portion of the ordinary income dividends for the Growth Fund, the Large Cap Growth Fund, the Mid Cap Growth Fund, the Small-Mid Cap Core Fund, the Small-Mid Cap Growth Fund, the Small-Mid Cap Value Fund, the Small Cap Growth Fund and the Small Cap Value Fund will be eligible for the dividends-received deduction available to corporate shareholders and for treatment as qualified dividend income available to individual and other non-corporate shareholders. A portion of the dividends of the Global Leaders Fund, the International Leaders Fund, the International Growth Fund, the Institutional International Growth Fund, the International Small Cap Growth Fund, the Emerging Markets Leaders Fund, the Emerging Markets Growth Fund and the Emerging Markets Small Cap Growth Fund may be eligible for treatment as qualified dividend income.

Taxes on Transactions. Redemptions of Fund shares and exchanges for shares of other William Blair Funds are generally treated as a sale of such shares subject to federal income taxation and possibly state and local taxation. If the shares are held as a capital asset, then you will recognize, subject to the discussion below, a capital gain or loss measured by the difference between your basis in your shares and the price that you receive when you sell (or exchange) such shares. The capital gain or loss upon a sale, exchange or redemption of Fund shares will generally be a short-term capital gain or loss if such shares were held for one year or less, and will be a long-term capital gain or loss if such shares were held for more than one year. Long-term capital gains are generally taxable to individuals and other non-corporate shareholders at a maximum federal income tax rate of 20%. Any loss recognized on the redemption of shares held six months or less, however, will be treated as a long-term capital loss to the extent you have received any long-term capital gain dividends on such shares. If you realize a loss on the redemption or exchange of Fund shares and acquire within 30 days before or after such redemption or exchange shares of the same Fund (including through reinvestment of dividends) or substantially identical stock or securities, the two transactions may be subject to the “wash sale” rules of the Code resulting in a postponement of the recognition of such loss for federal income tax purposes. Capital losses may be subject to limitations on their use by a shareholder.

An additional 3.8% Medicare contribution tax is imposed on certain net investment income (including income dividends and capital gain distributions received from a Fund and net gains from redemptions or other taxable dispositions of Fund shares) of U.S. individuals, estates and trusts to the extent that such person’s “modified adjusted gross income” (in the case of an individual) or “adjusted gross income” (in the case of an estate or trust) exceeds a threshold amount.

Effect of Foreign Taxes. Investment income received from sources within foreign countries may be subject to foreign income taxes, which generally will reduce a Fund’s distributions. However, the United States has entered into tax treaties with many foreign countries that entitle certain investors to a reduced rate of tax or to certain exemptions from tax. Accordingly, the Global Leaders Fund, the International Leaders Fund, the International Growth Fund, the Institutional International Growth Fund, the International Small Cap Growth Fund, the Emerging Markets Leaders Fund, the Emerging Markets Growth Fund and the Emerging Markets Small Cap Growth Fund will attempt to operate so as to qualify for such reduced tax rates or tax exemptions whenever

practicable. Additionally, the Global Leaders Fund, the International Leaders Fund, the International Growth Fund, the Institutional International Growth Fund, the International Small Cap Growth Fund, the Emerging Markets Leaders Fund, the Emerging Markets Growth Fund and the Emerging Markets Small Cap Growth Fund may each qualify for and may each elect to have foreign tax credits “passed through” to its shareholders. In such event, shareholders will be required to treat as part of the amounts distributed to them their pro rata portion of such taxes and may claim a federal income tax credit or a deduction for such taxes, subject to certain holding period and other limitations. No deduction for foreign taxes may be claimed by a shareholder who does not itemize deductions on his or her federal income tax return.

“Buying a Dividend.” If you buy shares before a Fund deducts a distribution from its net asset value, you will pay the full price for the shares and then receive a portion of the price back in the form of a distribution, which may be subject to federal income tax as described above. In addition, a Fund’s share price may, at any time, reflect undistributed capital gains or income and unrealized appreciation, which may result in future taxable distributions. Such distributions can occur even in a year when a Fund has a negative return. See “Your Account—Dividends and Distributions” for payment schedules, and call the Distributor if you have further questions.

Tax Withholding. The Funds may be required to withhold U.S. federal income tax at a rate of 24% on all distributions and redemption proceeds payable to shareholders who fail to provide their correct taxpayer identification number, fail to make certain required certifications or who have been notified (or when the Fund is notified) by the IRS that they are subject to backup withholding.

The foregoing is only intended as a brief summary of certain federal income tax issues relating to investment in a Fund by shareholders subject to federal income tax. Shareholders should consult their tax adviser about the application of the provisions of the tax laws, including state and local tax laws, in light of their particular situation before investing in a Fund.

For a more detailed discussion of federal income taxes, see the Statement of Additional Information.

The Funds provide a variety of services to help you manage your account. If you are investing through a financial intermediary, you may not have access to all of these services. You should consult with your intermediary directly to determine what services are available to you. Class R6 shares and the Institutional International Growth Fund may not be available through your financial intermediary.

Dividend Options. You may choose to have your distributions reinvested in additional shares automatically or paid in cash by making the appropriate election on your account application. You may change your election at any time by providing written notice to DST. Dividends and distributions are treated the same for federal income tax purposes whether reinvested in additional shares or received in cash.

1. Automatic Dividend Reinvestment Plan. The Funds automatically reinvest all income dividends and capital gain distributions in additional shares at net asset value on the reinvestment date. (For more information, see “Your Account—Dividends and Distributions.”)

2. Cash-Dividend Plan. You may choose to have all of your income dividends paid in cash and/or have your capital gain distributions paid in cash. Any distributions you do not elect to have paid in cash will be reinvested automatically in additional shares at net asset value.

3. Automatic Deposit of Dividends. You may elect to have all income dividends and capital gain distributions automatically deposited in a previously established bank account.

Automatic Investment Plan. On your account application for Class N shares or Class I shares of a Fund, you may authorize DST to automatically withdraw an amount of money (minimum $250) from your bank account on the fifth or twentieth day of each month. This amount will be invested in additional shares. You may change your election at any time by providing written notice to DST.

Systematic Withdrawal Plan. You may establish this plan with Class N shares or Class I shares presently held or through a new investment, which should be at least $2,500 for Class N shares and $500,000 for Class I shares. Under this plan, you specify a dollar amount to be paid monthly, quarterly or annually. Shares corresponding to the specified dollar amount are automatically redeemed from your account on the fifth business day preceding the end of the month, quarter or year. While this plan is in effect, all income dividends and capital gain distributions on shares in your account will be reinvested at net asset value in additional shares. There is no charge for withdrawals, but the minimum withdrawal is $250 per month. Depending upon the size of payments requested, and fluctuations in the net asset value of the shares redeemed, redemptions under this plan may reduce or even exhaust your account.

Retirement Plans and Other Plan Accounts. The Trust may offer a variety of qualified retirement plans and other tax-advantaged accounts, including employee benefit plans, Individual Retirement Accounts (“IRAs”), Roth IRAs, Simplified Employee Pension Plan IRAs (“SEP IRAs”), Savings Incentive Match Plan for Employees IRAs (“SIMPLE IRAs”), Health Savings Accounts, Archer Medical Savings Accounts, Coverdell Education Savings Accounts (formerly known as education IRAs) and Solo 401(k) Plans (collectively, “Retirement Plan and Other Plan Accounts”). Additional information concerning Retirement Plans and Other Accounts is available from the Trust.

For Class N shares, the minimum initial investment in a Retirement Plan and Other Plan Account generally is $2,500 and the minimum subsequent investment generally is $1,000. For Class I shares, there is no minimum initial investment for a Retirement Plan and Other Plan Account and there is no minimum for subsequent investments. Shareholders who open Retirement Plan and Other Plan Accounts may be charged additional fees by the custodian for the plan. With regard to Retirement Plan and Other Plan Accounts:

Written Confirmations. Each purchase, exchange or redemption transaction is confirmed in writing to the address of record by giving details of the purchase or redemption.

Transfer of Shares. Fund shares may be transferred by a written request addressed to the Trust and delivered to DST, giving the name and social security or taxpayer identification number of the transferee and accompanied by the same signature guarantees, if applicable, and documents as would be required for a redemption, together with specimen signatures of all transferees.

Suspension of Offering or Rejection of Purchase Orders. The Trust reserves the right to withdraw all or any part of the offering made by this Prospectus, and/or the Trust or the Distributor may reject purchase orders from an investor or an intermediary. From time to time, the Trust may suspend the offering of shares of a Fund to new investors. During the period of such suspension, persons who are already shareholders of a Fund may be permitted to continue to purchase additional shares of the Fund, to have dividends reinvested and to make redemptions. In addition, a Fund may be liquidated and terminated at any time without shareholder approval. Such a liquidation could have negative tax consequences for shareholders and will cause shareholders to incur expenses of liquidation.

Consultation With a Professional Tax Adviser is Recommended, both because of the complexity of federal tax laws and because various tax penalties are imposed for excess contributions to, and late or premature distributions from, IRAs or other qualified retirement plans. Termination of a plan shortly after its adoption may have adverse tax consequences.

Shareholder Rights. All shares of each Fund have equal rights with respect to dividends, assets and liquidation of a Fund and equal, noncumulative voting rights. Noncumulative voting rights allow the holder or holders of a majority of shares, voting together for the election of trustees, to elect all the trustees. All shares of the William Blair Funds will be voted in the aggregate, except when a separate vote by a William Blair Fund is required under the 1940 Act. Shares are fully paid and nonassessable when issued, are transferable without restriction, and have no preemptive or conversion rights. Under Delaware law, the Trust is not required to hold shareholder meetings on an annual basis. As required by law, the Funds will, however, hold shareholder meetings when a sufficient number of shareholders request a meeting, or as deemed desirable by the Board of Trustees, for such purposes as electing or removing trustees, changing fundamental policies or approving a material amendment to the Management Agreement. (For additional information about shareholder voting rights, see the Statement of Additional Information.)

Householding. In order to reduce the amount of mail you receive and to help reduce Fund expenses, the Trust generally sends a single copy of any shareholder report and prospectus to each household. If you do not want the mailing of these documents to be combined with those for other members of your household, please call 1-800-742-7272.

These charges could reduce your yield or return. In addition, when you place orders with an intermediary, you are not placing your orders directly with the Fund, and you must follow the intermediary’s transaction procedures. Your intermediary may impose different or additional conditions than the Fund on purchases, redemptions and exchanges of Fund shares. These differences may include different minimum initial (and subsequent) investment amounts, exchange policies, fund choices, cut-off times for investment and other trading restrictions. You should consult your intermediary directly for information regarding its conditions and fees. The Funds are not responsible for the failure of your intermediary to carry out its responsibilities.

A Fund’s net asset value is the value of its total assets minus its liabilities. A Fund’s net asset value per share is determined by dividing the Fund’s net asset value by the number of Fund shares outstanding.

The net asset value per share shall be determined as of the close of regular trading on the New York Stock Exchange (“NYSE”), which is generally 3:00 p.m., Central time (4:00 p.m., Eastern time), on each day when the NYSE is open. A Fund does not price its shares on days when the NYSE is closed for trading.

Quotations of foreign securities in foreign currencies are converted into the United States dollar equivalents at the prevailing market rates as computed by State Street Bank and Trust Company, the Funds’ custodian. Trading in securities on exchanges and over-the-counter markets in Europe and the Far East is normally completed at various times prior to 3:00 p.m., Central time, the current closing time of the NYSE. Trading on foreign exchanges may not take place on every day that the NYSE is open. Conversely, trading in various foreign markets may take place on days when the NYSE is not open and on other days when net asset value is not calculated. Consequently, the value of the net assets held by the Global Leaders Fund, the International Leaders Fund, the International Growth Fund, the Institutional International Growth Fund, the International Small Cap Growth Fund, the Emerging Markets Leaders Fund, the Emerging Markets Growth Fund and the Emerging Markets Small Cap Growth Fund may be significantly affected on days when shares are not available for purchase or redemption.

U.S. Equity Securities. The value of U.S. equity securities, including exchange-traded funds, is determined by valuing securities traded on national securities markets or in the over-the-counter markets at the last sale price or, if applicable, the official closing price or, in the absence of a recent sale on the date of determination, at the mean between the last reported bid and ask prices.

Foreign Equity Securities. The value of foreign equity securities is generally determined based upon the last sale price on the foreign exchange or market on which it is primarily traded and in the currency of that market as of the close of the appropriate exchange or, if there have been no sales during that day, at the mean between the last reported bid and ask prices. The Board of Trustees has determined that the passage of time between when the foreign exchanges or markets close and when a Fund computes its net asset value could cause the value of foreign equity securities to no longer be representative or accurate and, as a result, may necessitate that such securities be fair valued. Accordingly, for foreign equity securities, a Fund may use an independent pricing service to fair value price the security as of the close of regular trading on the NYSE in the event of market movement occurring after the close of regular trading on the foreign exchange or market where the security is primarily traded. As a result, a Fund’s value for a security may be different from the last sale price (or the mean between the last reported bid and ask prices).

Domestic and Foreign Fixed Income Securities. Fixed income securities are generally valued using evaluated prices provided by an independent pricing service or, if a price is not available, the security is valued at the mean between the last reported bid and the last reported ask obtained by an independent pricing service. The evaluated prices are formed using various market inputs that the pricing service believes accurately represent the market value of a security at a particular point in time. The pricing service determines evaluated prices for fixed income securities using inputs including, but not limited to, recent transaction prices, dealer quotes, transaction prices for securities with similar characteristics, collateral characteristics, credit quality, payment history, liquidity and market conditions. Repurchase agreements and certain privately placed debt securities are valued at cost, which approximates fair value.

extensively. Option contracts on foreign indices are valued at the settlement price. Futures contracts (and options and swaps thereon) are valued at the most recent settlement price on the exchange on which they are traded most extensively. Forward foreign currency contracts are valued on the basis of the value of the underlying currencies at the prevailing currency exchange rate as supplied by an independent pricing service.

Over-the-Counter (“OTC”) swap contracts are valued by an independent pricing service. Depending on the product and the terms of the transaction, the independent pricing service may use a series of techniques, including simulation pricing models. The pricing models use inputs that are observed from actively quoted markets such as issuer details, indices, spreads, interest rates, yield curves, dividends and exchange rates.

Centrally cleared swaps listed or settled on a multilateral or trade facility platform, such as a registered exchange, are valued at the daily settlement price determined by the respective exchange. For centrally cleared credit default swaps the clearing facility requires its members to provide actionable price levels across complete term structures. These levels along with external third-party prices are used to produce daily settlement prices.

Other Valuation Factors. Securities, and other assets, for which a market price is not available or is deemed unreliable (e.g., securities affected by unusual or extraordinary events, such as natural disasters or securities affected by market or economic events, such as bankruptcy filings), or the value of which is affected by a significant valuation event, are valued at a fair value as determined in good faith by, or under the direction of, the Board of Trustees and in accordance with the Trust’s valuation procedures. The value of fair valued securities may be different from the last sale price (or the mean between the last reported bid and ask prices), and there is no guarantee that a fair valued security will be sold at the price at which a Fund is carrying the security.

The following glossary explains some of the types of securities in which the Funds may invest, investment techniques they may employ, and some of the related risks. For more information, please see other sections of this prospectus, including the Summary, Additional Information Regarding Investment Objectives and Strategies, and Principal Risks, as well as the Statement of Additional Information.

Collateralized Obligations. Mortgage-Backed Securities. Mortgage-backed securities are securities that directly or indirectly represent a participation in, or are secured by and payable from, mortgage loans secured by real property. There currently are three basic types of mortgage-backed securities: (1) those issued or guaranteed by the U.S. Government or one of its agencies or instrumentalities, such as GNMA (Government National Mortgage Association), FNMA (Federal National Mortgage Association) and FHLMC (Federal Home Loan Mortgage Corporation); (2) those issued by private issuers that represent an interest in or are collateralized by mortgage-backed securities issued or guaranteed by the U.S. Government or one of its agencies or instrumentalities; and (3) those issued by private issuers that represent an interest in or are collateralized by whole mortgage loans or mortgage-backed securities without a government guarantee but that usually have some form of private credit enhancement.

Collateralized Mortgage Obligations (“CMOs”). A CMO is a debt obligation of a legal entity that is collateralized by mortgages and divided into classes. Similar to a bond, interest and prepaid principal is paid, in most cases, on a monthly basis. CMOs may be collateralized by whole mortgage loans or private mortgage bonds, but are more typically collateralized by portfolios of mortgage pass-through securities guaranteed by GNMA, FHLMC or FNMA, and their income streams.

CMOs are structured into multiple classes, often referred to as “tranches,” with each class bearing a different stated maturity and entitled to a different schedule for payments of principal and interest, including pre-payments. Actual maturity and average life will depend upon the pre-payment experience of the collateral. In the case of certain CMOs (known as “sequential pay” CMOs), payments of principal received from the pool of underlying mortgages, including pre-payments, are applied to the classes of CMOs in the order of their respective final distribution dates. Thus, no payment of principal will be made to any class of sequential pay CMOs until all other classes having an earlier final distribution date have been paid in full.

Asset-Backed Securities. Asset-backed securities are similar in structure to mortgage-backed securities but represent interests in pools of loans, leases or other receivables in place of mortgages. Asset-backed securities are primarily issued by non-government entities.

Mortgage-Backed To-Be-Announced (TBA) Securities. The Bond Fund, the Income Fund and the Low Duration Fund may engage in purchases and sales of mortgage-backed securities eligible to be sold in the to-be announced (TBA) market, which are transactions in which the Fund purchases or sells mortgage-backed securities on a forward commitment basis for delivery at a future date; however, the specific mortgage-backed securities to be delivered as part of the transaction are not identified until forty-eight hours prior to the settlement date. Mortgage-backed TBA securities can be used for hedging purposes to adjust the risk exposure of a portfolio without having to restructure the portfolio. Each Fund may “roll over” mortgage-backed TBA agreements prior

to the settlement date in a transaction sometimes referred to as a “TBA roll.” In a TBA roll, a Fund will sell the obligation to purchase the mortgage-backed securities in the TBA agreement prior to the settlement date and will enter into a new mortgage-backed TBA agreement.

Convertible Securities. Convertible securities are bonds, notes, debentures, preferred stock and other securities that are convertible into common stock. Convertible securities have general characteristics of both debt and equity securities. As debt securities, convertible securities are investments that provide a stream of income with generally higher yields than common stocks. Although to a lesser extent than with debt securities generally, the market value of convertible securities tends to decline as interest rates increase and conversely, tends to increase as interest rates decline. The Bond Fund will not convert or exchange convertible securities it owns into the underlying shares of common stock.

Depository Receipts. American Depository Receipts (“ADRs”) are dollar-denominated securities issued by a U.S. bank or trust company that represent, and may be converted into, the underlying foreign security. European Depository Receipts (“EDRs”) and Global Depository Receipts (“GDRs”) represent a similar securities arrangement but are issued by European banks or other depositories, respectively. ADRs, EDRs and GDRs may be denominated in a currency different from the underlying securities into which they may be converted. Typically, ADRs, in registered form, are designed for issuance in U.S. securities markets, and EDRs and GDRs, in bearer form, are designed for issuance in European securities markets. Investments in depository receipts entail risks similar to direct investments in foreign securities. These risks are detailed in the “Principal Risks” section above and in the Statement of Additional Information.

Derivatives. As described in the “Additional Information Regarding Investment Objectives and Strategies” section of this Prospectus, the Global Leaders Fund, the International Leaders Fund, the International Growth Fund, the Institutional International Growth Fund, the International Small Cap Growth Fund, the Emerging Markets Leaders Fund, the Emerging Markets Growth Fund, the Emerging Markets Small Cap Growth Fund, the Bond Fund, the Income Fund and the Low Duration Fund may use certain types of derivatives for hedging or risk management purposes as well as to equitize cash in situations involving large cash inflows or anticipated large redemptions. Derivatives are financial contracts whose value depends on, or is derived from, the value of an underlying asset, reference rate or index.

Futures. A futures contract provides for the future sale by one party and purchase by another party of a specified amount of a specific financial instrument, index, security or commodity for a specified price at a designated date, time and place. An index futures contract is an agreement pursuant to which the parties agree to take or make delivery of an amount of cash equal to the difference between the value of the index at the close of the last trading day of the contract and the price at which the index futures contract was originally written. Transaction costs are incurred when a futures contract is bought or sold and margin deposits must be maintained. A futures contract may be satisfied by delivery or purchase, as the case may be, of the instrument, security or commodity or by payment of the change in the cash value of the index. More commonly, futures contracts are closed out prior to delivery by entering into an offsetting transaction in a matching futures contract. If the offsetting purchase price is less than the original sale price, a Fund realizes a gain; if it is more, a Fund realizes a loss. Conversely, if the offsetting sale price is more than the original purchase price, a Fund realizes a gain; if it is less, a Fund realizes a loss. The transaction costs must also be included in these calculations. There can be no

assurance, however, that a Fund will be able to enter into an offsetting transaction with respect to a particular futures contract at a particular time.

Forward Foreign Currency Contracts. A forward foreign currency contract is an agreement to purchase or sell a specific currency at a specified future date and price agreed to by the parties at the time of entering into the contract. A forward currency contract is either settled by physical delivery of the commodity or tangible asset to an agreed-upon location at a future date, rolled forward into a new forward contract or, in the case of a non-deliverable forward, by a cash payment at maturity. A Fund may use forward foreign currency contracts to fix the value of certain securities it has agreed to buy or sell. For example, when a Fund enters into a contract to purchase or sell securities denominated in a particular foreign currency, the Fund could effectively fix the maximum cost of those securities by purchasing or selling a forward currency contract, for a fixed value of another currency, in the amount of foreign currency involved in the underlying transaction. A Fund may also use forward foreign currency contracts to hedge the value, in U.S. dollars, of securities it currently owns. For example, if a Fund held securities denominated in a foreign currency and anticipated a substantial decline (or increase) in the value of that currency against the U.S. dollar, the Fund may enter into a forward currency contract to sell (or purchase), for a fixed amount of U.S. dollars, the amount of foreign currency approximating the value of all or a portion of the securities held which are denominated in such foreign currency. Although forward foreign currency contracts minimize the risk of loss resulting from a decline in the value of the hedged currency, they also limit the potential for gain resulting from an increase in the value of the hedged currency. The benefits of forward foreign currency contracts to a Fund will depend on the ability of the Adviser to accurately predict future currency exchange rates.

Swaps. A swap is a customized, privately negotiated agreement that obligates two parties to exchange a series of cash flows at specified intervals (payment dates) based upon or calculated by reference to changes in specified process or rates (interest rates in the case of interest rate swaps, currency exchange rates in the case of currency swaps) for a specified amount of an underlying asset (the “notional” principal amount). Cleared swaps are transacted through futures commission merchants that are members of central clearinghouses with the clearinghouse serving as a central counterparty. The swaps market was largely unregulated prior to the enactment of the Dodd-Frank Wall Street Reform and Consumer Protection Act (the “Dodd-Frank Act”). Pursuant to rules promulgated under the Dodd-Frank Act, central clearing of swap agreements is currently required for certain market participants trading certain instruments, and central clearing for additional instruments is expected to be implemented by regulators until the majority of the swaps market is ultimately subject to central clearing.

Credit Default Swaps. A credit default swap is a contract between a buyer and a seller of protection against a pre-defined credit event (e.g., a ratings downgrade or default) on an underlying reference obligation, which may be a single debt instrument or baskets or indices of securities. Credit default swaps are used as a means of “buying” credit protection (i.e., attempting to mitigate the risk of default or credit quality deterioration in some portion of a Fund’s holdings) or “selling” credit protection (i.e., attempting to gain exposure to an underlying issuer’s credit quality characteristics without directly investing in that issuer). A Fund may be a buyer or seller of a credit default swap. Where a Fund is a seller of credit protection, it adds leverage to its portfolio because the Fund is subject to investment exposure on the notional amount of the swap which would be offset to the extent of its uncommitted cash or cash equivalents. A Fund will only sell credit protection with respect to securities in which it would be authorized to invest directly.

full notional amount, or “par value,” of the reference obligation and the market value of the reference obligation. Credit default swaps may involve greater risks than if a Fund had invested in the reference obligation directly. In addition to the risks applicable to derivatives generally, credit default swaps involve special risks because they may be difficult to value and may be more susceptible to liquidity and credit risk.

Emerging Markets. Emerging markets include every country in the world except the United States, Canada, Japan, Australia, New Zealand, Hong Kong, Singapore and most Western European countries. Emerging market companies are companies organized under the laws of an emerging market country or having securities that are traded principally on an exchange or over-the-counter in an emerging market country.

Hybrid Bonds. The Bond Fund may invest in hybrid bonds. Hybrid bonds are securities that have debt and equity characteristics. Like other bonds, hybrid bonds have periodic coupon payments and a stated maturity and the issuer pays interest pre-tax. Like equity securities, hybrid bonds fall below senior debt in an issuer’s capital structure and have features that allow the issuer to skip payments without defaulting.

Initial Public Offerings (“IPOs”). A Fund may participate in IPOs. IPOs are subject to high volatility and are of limited availability. A Fund’s ability to obtain allocations of IPOs is subject to allocation by members of the underwriting syndicate to various clients and allocation by the Adviser among its clients. When a Fund is small in size, the Fund’s participation in IPOs may have a magnified impact on the Fund’s performance.

Preferred Stock. Preferred stock has a preference over common stock in liquidation, but is subordinated to the liabilities of the issuer in all respects. Preferred stock may offer the opportunity for capital appreciation as well as periodic income.

Private Placements. A Fund may purchase securities in private placement transactions. Investments in private placements may be difficult to sell at the time and at the price desired by a Fund; companies making private placements may make less information available than publicly offered companies; and privately placed securities are more difficult to value than publicly traded securities. These factors may have a negative effect on the performance of a Fund. Securities acquired through private placements are not registered for resale in the general securities market and may be classified as illiquid.

Real Estate Investment Trusts (“REITs”). REITs are pooled investment vehicles that typically invest directly in real estate, in mortgages and loans collateralized by real estate, or in a combination of the two. “Equity” REITs invest primarily in real estate that produces income from rentals. “Mortgage” REITs invest primarily in mortgages and derive their income from interest payments. REITs usually specialize in a particular type of property and may concentrate their investments in particular geographical areas. REITs issue stocks and most REIT stocks trade on the major stock exchanges or over-the-counter. Exposure to real estate markets, through securities of REITs or other instruments, will be subject to risks of the specific properties or property types and by default rates of borrowers or tenants. Some REITs may have limited diversification and may be subject to risks inherent in investments in a limited number of properties, in a narrow geographic area, or in a single property type. Real estate is also affected by general economic conditions. When growth is slowing, demand for property decreases and prices may decline. Rising interest rates, which drive up mortgage and financing costs, can restrain construction and buying and selling activity, and may reduce the appeal of real estate investments. REITs depend generally on their ability to generate cash flow to make distributions to shareholders or unitholders, and may be subject to defaults by borrowers and self-liquidations. A REIT’s return may be adversely affected when interest rates are high or rising. Distributions to shareholders attributable to dividends received from REITs generally are taxed as ordinary income for federal income tax purposes. In addition, the failure of a REIT to continue to qualify as a REIT for federal income tax purposes would have an adverse effect upon the value of an investment in that REIT.

Repurchase Agreements. Repurchase agreements are instruments under which a Fund acquires ownership of a security, and the seller, a broker-dealer or a bank agrees to repurchase the security at a mutually agreed upon

time and price. The repurchase agreement serves to fix the yield of the security during a Fund’s holding period. The Funds currently intend to enter into repurchase agreements only with member banks of the Federal Reserve System or primary dealers in U.S. Government securities and that are cleared through the Fixed Income Clearing Corporation (“FICC”). In all cases, the Adviser must be satisfied with the creditworthiness of the seller before entering into a repurchase agreement. In the event of the bankruptcy or other default of the seller of a repurchase agreement, a Fund could incur expenses and delays enforcing its rights under the agreement, and experience a decline in the value of the underlying securities and loss of income. The maturity of a security subject to repurchase may exceed one year, and, for the Income Fund, the modified duration of a security subject to repurchase may exceed nine years. Repurchase agreements maturing in more than seven days, together with any securities that are restricted as to disposition under the federal securities laws or are otherwise considered to be illiquid, will not exceed 15% of the net assets of each Fund.

Rule 144A Securities. Rule 144A securities are restricted securities that can be sold to qualified institutional buyers under the Securities Act of 1933, as amended. Investing in Rule 144A securities may increase the illiquidity of a Fund’s investments in the event that an adequate trading market does not exist for these securities.

Section 4(2) Paper. The Low Duration Fund may invest in commercial paper issued in reliance upon the so-called “private placement” exemption from registration afforded by Section 4(2) of the Securities Act of 1933 (“Section 4(2) paper”). The Bond Fund may also invest in Section 4(2) paper from time to time in connection with certain mortgage-backed transactions. Section 4(2) paper is restricted as to disposition under the federal securities laws, and generally is sold to institutional investors such as the Fund. Any resale by the purchaser must be in an exempt transaction. Section 4(2) paper normally is resold to other institutional investors through or with the assistance of the issuer or investment dealers who make a market in the Section 4(2) paper, thus providing liquidity. The Adviser considers the legally restricted but readily saleable Section 4(2) paper to be liquid; however, pursuant to the procedures approved by the Fund’s Board of Trustees, if a particular investment in Section 4(2) paper is not determined to be liquid, that investment will be included within the limitation on illiquid securities.

U.S. Government Securities. These are fixed income obligations of the U.S. Government and its various agencies. U.S. Government securities issued by the U.S. Treasury (bills, notes and bonds) are backed by the full faith and credit of the federal government. Some government securities not issued by the U.S. Treasury also carry the U.S. Government’s full faith and credit backing on principal or interest payments. Some securities are backed by the issuer’s right to borrow from the U.S. Treasury, and some are backed only by the credit of the issuing organization. All U.S. Government securities are considered highly creditworthy. This guarantee, however, does not extend to the market prices for such securities, which can fluctuate.

Variable Rate Securities. The Bond Fund, the Income Fund and the Low Duration Fund may invest in instruments having rates of interest that are adjusted periodically or that “float” continuously or periodically according to formulae intended to minimize fluctuation in values of the instruments (“Variable Rate Securities”). The interest rate on a Variable Rate Security is ordinarily determined by reference to, or is a percentage of, an objective standard such as the London Interbank Offered Rate (LIBOR), a bank’s prime rate, the 90-day U.S. Treasury Bill rate or the rate of return on commercial paper or bank certificates of deposit. Generally, the changes in the interest rates on Variable Rate Securities reduce the fluctuation in the market value of such securities. Accordingly, as interest rates decrease or increase, the potential for capital appreciation or depreciation is less than for fixed-rate obligations. A Fund may invest in Variable Rate Securities that have a demand feature entitling a Fund to resell the securities to the issuer or a third party at an amount approximately equal to the principal amount thereof plus accrued interest (“Variable Rate Demand Securities”). As is the case for other Variable Rate Securities, the interest rate on Variable Rate Demand Securities varies according to some objective standard intended to minimize fluctuation in the values of the instruments. Many of these Variable Rate Demand Securities are unrated, their transfer is restricted by the issuer and there is little if any secondary market for the securities. Thus, any inability of the issuers of such securities to pay on demand could adversely affect the liquidity of these securities. A Fund determines the maturity of Variable Rate Securities in accordance with

Securities and Exchange Commission rules, which allow a Fund to consider certain of such instruments as having maturities shorter than the maturity date on the face of the instrument if they are guaranteed by the U.S. Government or its agencies, if they have a stated maturity date of one year or less, or if they have demand features prior to maturity.

Warrants. Warrants are securities giving the holder the right, but not the obligation, to buy the stock of an issuer at a given price (generally higher than the value of the stock at the time of issuance) during a specified period or perpetually. Warrants may be acquired separately or in connection with the acquisition of securities. Warrants do not carry with them the right to dividends or voting rights with respect to the securities that they entitle their holder to purchase and they do not represent any rights in the assets of the issuer. As a result, warrants may be considered to have more speculative characteristics than certain other types of investments. In addition, the value of a warrant does not necessarily change with the value of the underlying securities and a warrant ceases to have value if it is not exercised prior to its expiration date.

When-Issued and Delayed Delivery Securities. From time to time, in the ordinary course of business, a Fund may purchase newly issued securities appropriate for the Fund on a “when-issued” basis, and may purchase or sell securities appropriate for the Fund on a “delayed delivery” basis. When-issued or delayed delivery transactions involve a commitment by a Fund to purchase or sell particular securities, with payment and delivery to take place at a future date. These transactions allow a Fund to lock in an attractive purchase price or yield on a security the Fund intends to purchase. Normally, settlement occurs within one month of the purchase or sale. During the period between purchase and settlement, no payment is made or received by a Fund and, for delayed delivery purchases, no interest accrues to a Fund. Because a Fund is required to set aside cash or liquid securities at least equal in value to its commitments to purchase when-issued or delayed delivery securities, the Adviser’s ability to manage the Fund’s assets may be affected by such commitments. A Fund will only make commitments to purchase securities on a when-issued or delayed delivery basis with the intention of actually acquiring the securities, but it reserves the right to sell them before the settlement date if it is deemed advisable.

The tables below are intended to help you understand each Fund’s financial performance for the fiscal periods presented. Certain information reflects financial results for a single Fund share. The total return figures show what an investor in a Fund would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the financial statements audited by Ernst & Young LLP, whose report, along with the Funds’ financial statements, is included in the annual report dated December 31, 2019, which is available upon request (see back cover). Net investment income (loss) per share is based on the average shares outstanding during the year.

More information about the Funds is available without charge, upon request, including the following:

The Semi-Annual and audited Annual Reports to shareholders include financial statements, detailed performance information, portfolio holdings and statements from the Fund managers. In the Annual Report, you will find a discussion of the market conditions and investment strategies that the Adviser believes significantly affected each Fund’s performance in its last fiscal year.

The SAI contains more detailed information about the Funds. The current SAI has been filed with the Securities and Exchange Commission and is incorporated by reference into this Prospectus, which means that it is part of this Prospectus for legal purposes.

Text-only versions of Fund documents can be viewed online or downloaded from the EDGAR Database on the SEC’s Internet site at www.sec.gov.

Reports and other information about the Funds are available on the EDGAR database of the SEC’s internet site at http://www.sec.gov. You may obtain copies of these reports and other information, after paying a duplicating fee, by sending an e-mail request to: publicinfo@sec.gov.

Reports and other information about the Funds are also available on the William Blair Funds website at: https://www.williamblairfunds.com/investor_services/prospectus_reports_forms.fs.

No person has been authorized to give any information or to make any representations not contained in this Prospectus and, if given or made, such information or representations must not be relied upon as having been authorized by the Trust or the Distributor. The Prospectus does not constitute an offering by the Trust or the Distributor in any jurisdiction in which such offering may not lawfully be made.

The Trust’s information, including but not limited to the Prospectus, SAI, Semi-Annual and Annual Reports and account application, can be viewed online at www.williamblairfunds.com.

The Securities and Exchange Commission and the Commodity Futures Trading Commission have not approved or disapproved these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

INVESTMENT OBJECTIVE: The William Blair Macro Allocation Fund (the “Fund”) seeks to maximize long-term risk-adjusted total return.

FEES AND EXPENSES: This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment):

Example: This example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The example also assumes that your investment has a 5% return each year and the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

PRINCIPAL INVESTMENT STRATEGIES: In pursuing the Fund’s investment objective, the Adviser employs dynamic, global macro asset and currency allocation strategies. These strategies attempt to exploit periodic market inefficiencies by taking long and short positions in various asset classes (e.g., equity and fixed income) (“market-oriented strategies”) and currencies (“currency-oriented strategies”) with a view to profit from movements across and within such asset classes and currencies. The Adviser uses a top-down approach that focuses on general price movements in various asset classes and currencies rather than the performance of individual company securities. The Adviser’s macro asset and currency management strategies are based primarily on the fundamental investment valuations of asset classes and currencies. The Adviser believes that investment fundamentals determine both future cash flows, which will ultimately drive the value of asset classes,

and relative purchasing power, which will ultimately drive the value of currencies. The Adviser’s goal is to identify and exploit periodic discrepancies between fundamental values and current prices. These perceived value/price discrepancies are the foundation for the Fund’s portfolio construction. In managing the Fund, the Adviser seeks to achieve a total rate of return (net of fees) that meets or exceeds the Consumer Price Index—All Urban Consumers (seasonally adjusted) plus 5% over a full market cycle (typically 6 to 10 years). The Adviser does not represent or guarantee that the Fund will meet this total return goal.

The Fund may invest in or seek exposure to a wide range of asset classes including, without limitation, equity, fixed income (including asset-backed securities, mortgage-backed securities and other collateralized obligations and all grades and maturities of domestic and foreign credit, including below-investment-grade securities (commonly referred to as “high yield” or “junk” bonds), commodities and real estate, and currencies. The Fund has no geographic or other limits on the allocation of its assets among asset classes. The Fund may invest its assets in any markets, including emerging markets, or asset classes that the Adviser believes to be appropriate for meeting the Fund’s investment objective. The Fund may also seek exposure to broad-based market indices, more narrowly focused customized trades or economic variables such as inflation rates. The Fund may seek long exposure to asset classes and currencies that the Adviser perceives will provide relatively attractive risk-adjusted returns and short exposure to asset classes and currencies that the Adviser perceives will provide relatively unattractive risk-adjusted returns, consistent with the Fund’s investment objective of maximizing long-term risk-adjusted total return. The Fund may also use long and short exposures to manage risk.

There are many ways in which the Fund may obtain a desired long exposure. The Fund may take long positions indirectly through exchange-traded funds (“ETFs”), exchange-traded notes and derivative instruments such as, but not limited to, futures, swaps, options and currency forward contracts. There are many ways in which the Fund may obtain a desired short exposure. The Fund may take short positions indirectly through ETFs, including inverse ETFs, and derivative instruments (listed above) that are intended to provide inverse exposure to a particular asset class or currency. Futures would typically be on, though are not limited to, equity indices and government bonds. Swaps would typically be on, though are not limited to, equity indices, including custom equity indices, equity index volatility/variance, government bonds, credit default indices, interest rates, inflation, commodities and commodity indices. The Fund may also enter into credit default swaps, including as the seller of a credit default swap. Options would typically be on, though are not limited to, equity indices, equity index futures, fixed income indices, government bonds, government bond futures and currencies. The Fund may also invest in individual stocks, real estate investment trusts, closed-end funds, preferred stock, publicly traded partnerships, royalty income trusts, repurchase agreements and other equity securities, fixed income securities and currencies for the purpose of effecting macro strategies. The Fund may engage in short sales on ETFs and individual securities. Long positions and short positions may be intended to enhance expected return, reduce expected risk, or both.

The Fund may increase or decrease its risk exposures by increasing and decreasing leverage, or by increasing and decreasing cash and cash equivalents. Leverage may be used to achieve potentially higher returns through proportionally higher ex-ante risk exposures. Ex-ante risk exposure is the Adviser’s forward-looking, best estimate, of the Fund’s standard deviation from an expected return. Leverage would increase the expected return when opportunities are anticipated to be greater than normal, but will also increase risk.

PRINCIPAL RISKS: The following is a summary of the principal risks associated with an investment in the Fund. The Fund may be subject to the following risks directly through investment in individual securities or indirectly through various instruments in which the Fund may invest, including ETFs, exchange-traded notes or derivative instruments.

The Fund involves a high level of risk and may not be appropriate for everyone. You could lose money by investing in the Fund. There can be no assurance that the Fund’s investment objective will be achieved. The Fund is not intended to be a complete investment program. The Fund is designed for long-term investors.

The principal risks of investing in the Fund (in alphabetical order after the first eight risks) are:

Asset Allocation Risk. In allocating the Fund’s assets, the Adviser may favor markets or asset classes that perform poorly relative to other markets and asset classes.

to value accurately. Some derivatives are more sensitive to market price fluctuations and to interest rate changes than other investments. The Fund also could suffer losses related to its derivatives positions as a result of unanticipated market movements, which losses are potentially unlimited. The Fund also may be exposed to losses if the counterparty in the transaction does not fulfill its contractual obligation. In addition, derivatives traded over-the-counter (“OTC derivatives”) do not benefit from the protections provided by exchanges in the event that a counterparty is unable to fulfill its contractual obligation. Such OTC derivatives therefore involve greater counterparty and credit risk and may be more difficult to value than exchange-traded derivatives. When a derivative is used as a hedge against a position that the Fund holds, any loss generated by the derivative should generally be offset by gains on the hedged instrument, and vice versa. While hedging can reduce or eliminate losses, it also can reduce or eliminate gains. Hedges are sometimes subject to imperfect matching between the derivative and the hedged investment, and there can be no assurance that the Fund’s hedging transactions will be effective. Also, suitable derivative transactions may not be available in all circumstances. Derivatives are subject to fees and other costs which are not reflected in the Annual Fund Operating Expenses table.

Aggressive Investment Technique Risk. The Fund may use investment techniques and financial instruments that may be considered aggressive, including but not limited to the use of futures contracts, options on futures contracts, securities and indices, forward contracts, swap agreements and similar instruments. Such techniques may also include short sales, taking short positions or using other techniques that are intended to provide inverse exposure to a particular market or other asset class, as well as leverage, which can expose the Fund to potentially dramatic losses or gains. These techniques may expose the Fund to potentially dramatic losses in the value of certain of its portfolio holdings.

Exchange-Traded and Closed-End Fund Risk. The risks of investment in other investment companies typically reflect the risk of the types of securities in which the other investment companies invest. Investments in ETFs and closed-end funds are subject to the additional risk that shares of the ETF or closed-end fund may trade at a premium or discount to their net asset value per share. When the Fund invests in another investment company, shareholders of the Fund bear their proportionate share of the other investment company’s fees and expenses as well as their share of the Fund’s fees and expenses. There may also not be an active trading market available for shares of some ETFs or closed-end funds. Additionally, trading of ETF and closed-end fund shares may be halted and ETF and closed-end fund shares may be delisted by the listing exchange.

Commodity Risk. Investing in commodities may subject the Fund to greater volatility than investments in traditional securities. The commodities markets have experienced periods of extreme volatility and future market conditions may result in rapid and substantial valuation increases and decreases. The value of commodities and commodity contracts may be affected by a variety of factors, including global supply and demand, changes in interest rates, commodity index volatility, and factors affecting a particular industry or commodity, such as drought, floods, weather, livestock disease, embargos, government regulation, tariffs and taxes, world events and economic, political and regulatory developments. Certain commodities or natural resources may be produced in a limited number of countries and may be controlled by a small number of producers. Political, economic and supply-related events in such countries could have a significant impact on the value of such commodities.

Credit Default Swap Risk. Credit default swaps are subject to the credit risk of the underlying reference obligation and to counterparty credit risk. If the counterparty fails to meet its obligations, the Fund may lose money. Credit default swaps are also subject to the risk that the Adviser will not properly assess the risk of the underlying reference obligation. If the Fund is selling credit protection, there is a risk that a credit event will occur and that the Fund will have to pay the counterparty. If the Fund is buying credit protection, there is a risk that no credit event will occur and the Fund will receive no benefit for the premium paid. Credit default swaps may be difficult to value and may have the effect of leverage on the Fund.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations.

Exchange-Traded Note Risk. The returns of exchange-traded notes (“ETNs”) are based on the performance of a specified market index minus applicable fees. The risks of ETNs include the risk of the reference index. The value of an ETN is also subject to the credit risk of the issuer. Thus, the value of an ETN may drop due to a decline in an issuer’s credit quality or a downgrade in the issuer’s credit rating, even if there is no change or an increase in the reference index. ETNs are subject to the additional risk that notes may trade at a premium or discount to their reference index. When the Fund invests in an ETN, shareholders of the Fund bear their proportionate share of the ETN’s fees and expenses as well as their share of the Fund’s fees and expenses. There may also not be an active trading market available for some ETNs. Additionally, trading of ETNs may be halted and ETNs may be delisted by the listing exchange.

Inverse ETF Risk. An inverse ETF is a fund that is constructed by using various derivative instruments to profit from a decline in the underlying benchmark. Investing in these ETFs is similar to holding various short positions, or using a combination of advanced investment strategies to profit from falling prices. Short sale risk involves the risk that the inverse ETF may incur a loss by subsequently buying a security at a higher price than the price at which it previously sold the security short. Because a loss incurred by an inverse ETF on a short sale results from increases in the value of the security, such losses are theoretically unlimited. An investment in an inverse ETF could result in a loss of the entire investment in that particular ETF. To the extent the inverse ETF uses derivatives to achieve short exposure, it is subject to derivatives risk including the risk of leverage.

use of leveraged investments may also cause the Fund to liquidate portfolio positions when it would not be advantageous to do so in order to satisfy its obligations or to meet asset segregation requirements. The use of leveraged investments may also cause the Fund to have higher expenses than those of mutual funds that do not use such techniques.

LIBOR Transition Risk. The Fund may invest in securities or derivatives that are based on the London Interbank Offered Rate (LIBOR). LIBOR transition risk is the risk that the transition from LIBOR to alternative interest rate benchmarks is not orderly, occurs over various time periods or has unintended consequences.

Mortgage-Backed/Asset-Backed Securities Risk. The Fund’s investments in mortgage-backed securities and asset-backed securities are subject to prepayment and extension risk. Prepayment of high interest rate mortgage-backed securities and asset-backed securities during times of declining interest rates will tend to lower the return of the Fund and may even result in losses to the Fund if the prepaid securities were acquired at a premium. Slower prepayments during periods of rising interest rates may increase the duration of the Fund’s mortgage-backed securities and asset-backed securities and reduce their value.

Private Placement Risk. Investments in private placements may be difficult to sell at the time and at the price desired by the Fund; companies making private placements may make less information available than publicly offered companies; and privately placed securities are more difficult to value than publicly traded securities. These factors may have a negative effect on the performance of the Fund. Securities acquired through private placements are not registered for resale in the general securities market and may be classified as illiquid.

Real Estate Risk. Exposure to real estate markets, through securities of real estate investment trusts (“REITs”) or other instruments, will be subject to risks of the specific properties or property types and by default rates of borrowers or tenants. Some REITs may have limited diversification and may be subject to risks inherent in investments in a limited number of properties, in a narrow geographic area, or in a single property type. Real estate is also affected by general economic conditions. When growth is slowing, demand for property decreases and prices may decline. Rising interest rates, which drive up mortgage and financing costs, can restrain construction and buying and selling activity, and may reduce the appeal of real estate investments. REITs depend generally on their ability to generate cash flow to make distributions to shareholders or unitholders, and may be subject to defaults by borrowers and self-liquidations. A REIT’s return may be adversely affected when interest rates are high or rising. Distributions to shareholders attributable to dividends received from REITs generally are taxed as ordinary income for federal income tax purposes.

Regulatory Risk. Future regulatory developments could impact the Fund’s ability to invest in certain derivatives. It is possible that government regulation of various types of derivative instruments, including futures, options and swap agreements, may limit or prevent the Fund from using such instruments as a part of its investment strategies, and could ultimately prevent the Fund from being able to achieve its investment objective. It is impossible to predict the effects of future legislation and regulation in this area, but the effects could be substantial and adverse. It is possible that legislative and regulatory activity could limit or restrict the ability of the Fund to use certain derivatives as a part of its investment strategies and could alter, perhaps to a material extent, the nature of an investment in the Fund or the ability of the Fund to continue to implement its investment strategies.

the establishment of daily price limits and the suspension of trading. The regulation of futures, options and swaps transactions in the United States is a changing area of law and is subject to modification by government and judicial action.

Short Position Risk. The Fund will incur a loss as a result of a short position in a financial instrument if the price of the financial instrument increases in value between the date the short position is established and the date on which the Fund enters into an offsetting transaction. Short positions may be considered speculative transactions and involve special risks. The Fund’s losses are potentially unlimited in a short position transaction.

Short Sales Risk. Short sales involve the risk that the Fund will incur a loss by subsequently buying a security at a higher price than the price at which the Fund previously sold the security short. Any loss will be increased by the amount of compensation, dividends or interest the Fund must pay to the lender of the security. Because a loss incurred by the Fund on a short sale results from increases in the value of the security, losses on a short sale are theoretically unlimited. In addition, the Fund may not be able to close out a short position at a particular time or at an acceptable price. A lender may request that borrowed securities be returned on short notice, and the Fund may have to buy the securities sold short at an unfavorable price. If this occurs at a time when other short sellers of the same security want to close out their positions, it is more likely that the Fund would have to close out its short position at an unfavorable price. If the Fund takes both long and short positions, there is a risk that the value of securities held long might decrease and the value of securities sold short might increase in response to activities of an individual company or general market conditions. In this case, the Fund’s potential losses could exceed those of mutual funds that hold only long positions.

Smaller Company Risk. Securities of smaller companies involve greater risk than those of larger, more established companies. This is because smaller companies may be in earlier stages of development, may be dependent on a small number of products or services, may lack substantial capital reserves and/or do not have proven track records. Smaller companies may be more adversely affected by poor economic or market conditions, and may be traded in low volumes, which may increase volatility and liquidity risks. From time to time, the Fund may invest in the equity securities of very small cap companies, often referred to as “micro-cap” companies. For purposes of the Fund, “micro-cap” companies are those with market capitalizations of $500 million or less at the time of the Fund’s investment. The considerations noted above are generally intensified for these investments.

Tax Risk. In order for the Fund to qualify as a regulated investment company under Subchapter M of the Internal Revenue Code of 1986, as amended, the Fund must derive at least 90% of its gross income each taxable year from certain qualifying sources of income (“qualifying income”). The Fund’s intention to qualify as a regulated investment company may limit its ability to make certain investments including, without limitation, investments in certain commodity-linked derivatives, since income from commodity-linked derivatives may not constitute qualifying income to the Fund. Receipt of such income could cause the Fund to fail to qualify as a regulated investment company and be subject to U.S. federal income tax on its taxable income at corporate rates.

FUND PERFORMANCE HISTORY: The information below provides some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for the periods indicated compare with those of a broad measure of market performance. The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. For more recent performance information, go to www.williamblairfunds.com or call 1-800-635-2886.

Annual Total Returns. The bar chart below provides an illustration of how the Fund’s performance has varied in each of the calendar years since the Fund started for Class N shares.

Average Annual Total Returns (For the periods ended December 31, 2019). The table below shows returns on a before-tax and after-tax basis for Class N shares and on a before tax basis for Class I and Class R6 shares. After-tax returns for Class I and Class R6 shares will vary. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. In some instances, the “Return After Taxes on Distributions and Sale of Fund Shares” may be greater than the “Return Before Taxes” because the investor is assumed to be able to use the capital loss on the sale of Fund shares to offset other taxable capital gains. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown. After-tax returns are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Investment Adviser. William Blair Investment Management, LLC is the investment adviser of the Fund.

Portfolio Manager(s). Brian D. Singer, a Partner of the Adviser, and Thomas Clarke, a Partner of the Adviser, co-manage the Fund. Messrs. Singer and Clarke have each co-managed the Fund since its inception in 2011.

Class I Share Purchase. The minimum initial investment for an account generally is $500,000 (or any lesser amount if, in William Blair’s opinion, the investor has adequate intent and availability of funds to reach a future level of investment of $500,000). There is no minimum for subsequent purchases. There is no minimum initial investment for qualified retirement plans, including, but not limited to, 401(k) plans, 457 plans, employer-sponsored 403(b) plans, defined benefit plans and other similar accounts, or plans whereby Class I shares are held through omnibus accounts (either at the plan level or the level of the plan administrator) and certain other accounts. The Distributor may make certain additional exceptions to the minimum initial investment amount in its discretion. Class I shares are only available to certain investors. See “Your Account—Class I Shares” for additional information on the eligibility requirements and investment minimums applicable to purchasing Class I shares.

Class R6 Share Purchase. The minimum initial investment for an account is $1 million (or any lesser amount if, in William Blair’s opinion, the investor has adequate intent and availability of funds to reach a future level of investment of $1 million). There is no minimum for subsequent purchases. There is no minimum initial investment for qualified retirement plans, including, but not limited to, 401(k) plans, 457 plans, employer-sponsored 403(b) plans, defined benefit plans and other similar accounts, or plans whereby Class R6 shares are held through omnibus accounts (either at the plan level or the level of the plan administrator) and certain other accounts. The Distributor may make certain additional exceptions to the minimum initial investment amount in its discretion. Class R6 shares are only available to certain investors. See “Your Account—Class R6 Shares” for additional information on eligibility requirements and investment minimums applicable to purchasing Class R6 shares.

Sale. Shares of the Fund are redeemable on any day the NYSE is open for business by mail, wire or telephone, depending on the elections you make in the account application.

The Summary Section describes the Fund’s principal investment policies and strategies intended to achieve its investment objective. The investment types discussed in the Summary Section are further described in the Investment Glossary contained herein and in the Statement of Additional Information.

Temporary Defensive Position. The Fund may significantly alter its make-up as a temporary defensive strategy. A defensive strategy will be employed only if, in the judgment of the Adviser, investments in the Fund’s usual markets or types of securities become decidedly unattractive because of current or anticipated adverse economic, financial, political and social factors. For temporary defensive purposes, the Fund may invest up to 100% of its assets in other types of securities, including high-quality commercial paper, obligations of banks and savings institutions, U.S. Government securities, government agency securities and repurchase agreements, or it may retain funds in cash. When the Fund is invested defensively, it may not meet its investment objective.

Portfolio Turnover. The Fund will adjust its portfolio as considered advisable in view of prevailing or anticipated market conditions and the Fund’s investment objective, and there is no limitation on the length of time securities must be held by the Fund prior to being sold. Portfolio turnover rate will not be a limiting factor for the Fund. Higher portfolio turnover rates involve correspondingly higher transaction costs, which are borne directly by the Fund. In addition, the Fund may realize significant short-term and long-term capital gains, which will result in taxable distributions to investors that may be greater than those made by other funds. Tax and transaction costs may lower the Fund’s effective return for investors.

Portfolio Holdings. A description on the policies and procedures with respect to the disclosure of the Fund’s portfolio securities is available in the Statement of Additional Information.

Use of Subsidiary. The Fund may seek exposure to the commodities markets by investing a portion of its assets in William Blair MAS Ltd., a wholly owned subsidiary of the Fund organized under the laws of the Cayman Islands (the “Subsidiary”). The Adviser, as part of its overall advisory services to the Fund, manages the investment and reinvestment of the assets of the Subsidiary and administers the affairs of the Subsidiary. The Adviser receives no additional compensation for providing management and administrative services to the Subsidiary. In managing the assets of the Subsidiary, the Adviser applies the Fund’s investment policies and restrictions and the Fund’s compliance policies and procedures generally as if such assets were held directly by the Fund. The financial statements of the Subsidiary will be consolidated with the financial statements of the Fund and the consolidated financial statements will be included in the Fund’s annual and semi-annual reports to shareholders. As of the date of this Prospectus, the Subsidiary is not operational and the Fund is not currently investing in the Subsidiary.

Investments by the Fund in the Subsidiary are expected to provide exposure to the commodities markets within the limitations of Subchapter M of the Internal Revenue Code of 1986, as amended (the “Code”). In order to qualify for the special tax treatment accorded regulated investment companies and their shareholders under the Code, the Fund must, among other things, satisfy certain diversification requirements, including the requirement that not more than 25% of the value of the Fund’s total assets may be invested in the securities (other than those of the U.S. Government or other regulated investment companies) of any one issuer or of two or more issuers which the Fund controls and which are engaged in the same, similar or related trades or businesses. Therefore, so long as the Fund is subject to this limit, the Fund may not invest any more than 25% of the value of its total assets in the Subsidiary. In addition, in order to qualify for the special tax treatment accorded regulated investment companies and their shareholders under the Code, the Fund must, among other things, derive at least 90% of its gross income from certain specified sources (“qualifying income”). Income from certain commodities

and commodity-linked derivatives does not constitute qualifying income to the Fund. If the Fund treats income from a particular instrument as qualifying income and the income is later determined not to constitute qualifying income, and, together with any other non-qualifying income, causes the Fund’s non-qualifying income to exceed 10% of its gross income in any taxable year, the Fund will fail to qualify as a regulated investment company unless it is eligible to and does pay a tax at the fund level.

Additional Information About the Fund. The Fund is a series of William Blair Funds, an open-end management investment company. The Adviser provides management and investment advisory services to the Fund. This prospectus doesn’t tell you about every policy or risk of investing in the Fund. If you want more information on the Fund’s allowable securities and investment practices and the characteristics and risks of each one, you may want to request a copy of the Statement of Additional Information (the back cover tells you how to do this).

The following is a description of the principal risks associated with an investment in the Fund. The Fund may be subject to the following risks directly through investment in individual securities or indirectly through various instruments in which the Fund may invest, including ETFs, exchange-traded notes and derivative instruments.

Asset Allocation Risk. In allocating the Fund’s assets, the Adviser may favor markets or asset classes that perform poorly relative to other markets and asset classes.

Commodity Risk. Investing in commodities may subject the Fund to greater volatility than investments in traditional securities. The commodities markets have experienced periods of extreme volatility and future market conditions may result in rapid and substantial valuation increases and decreases. The value of commodities and commodity contracts may be affected by a variety of factors, including global supply and demand, changes in interest rates, commodity index volatility, and factors affecting a particular industry or commodity, such as drought, floods, weather, livestock disease, embargos, government regulation, tariffs and taxes, world events and economic, political and regulatory developments. Certain commodities or natural resources may be produced in a limited number of countries and may be controlled by a small number of producers. Political, economic and supply -related events in such countries could have a significant impact on the value of such commodities.

Counterparty and Contractual Default Risk. The Fund’s investments in derivatives and other financial instruments that involve counterparties subject the Fund to the risk that the counterparty could default on its obligations under the agreement, either through the counterparty’s failure or inability to perform its obligations or bankruptcy. In the event of default, the Fund could experience lengthy delays in recovering some or all of its assets as a result of bankruptcy or other reorganization proceedings. The Fund could also experience limited recoveries or no recovery at all, and the value of an investment in the Fund could decline as a result. In addition, the Fund may default under an agreement with a counterparty which could adversely affect the Fund’s investing activities.

Credit Default Swap Risk. Credit default swaps are subject to the credit risk of the underlying reference obligation and to counterparty credit risk. If the counterparty fails to meet its obligations, the Fund may lose money. Credit default swaps are also subject to the risk that the Adviser will not properly assess the risk of the underlying reference obligation. If the Fund is selling credit protection, there is a risk that a credit event will occur and that the Fund will have to pay the counterparty. If the Fund is buying credit protection, there is a risk that no credit event will occur and the Fund will receive no benefit for the premium paid. Credit default swaps may be difficult to value and may have the effect of leverage on the Fund.

Credit Risk. The value of the Fund’s fixed income securities is subject to the ability of the issuers of such securities to make interest payments or payment at maturity. The credit ratings of issuers could change and negatively affect the Fund’s share price or yield.

Not all securities issued or guaranteed by agencies or instrumentalities of the U.S. Government are backed by the full faith and credit of the United States. Such securities involve different degrees of government backing. Some obligations issued or guaranteed by U.S. Government agencies or instrumentalities in which the Fund may invest are backed by the full faith and credit of the United States, such as modified pass-through certificates issued by

the Government National Mortgage Association, while others are backed exclusively by the agency or instrumentality with limited rights of the issuer to borrow from the U.S. Treasury. Others are backed only by the credit of the issuer itself. While the U.S. Government may provide financial support to such agencies or instrumentalities, no assurance can be given that it will always do so since it is not so obligated by law.

The Fund’s investments in below-investment-grade securities (e.g., high yield or junk bonds) may have additional credit risk. Securities rated BBB or below by a nationally recognized statistical rating organization have speculative characteristics and can be more vulnerable to bad economic news than investment grade securities, which could lead to a weakened capacity to make principal and interest payments. In some cases, below-investment-grade securities may decline in credit quality or go into default.

Derivatives Risk. Investing in derivatives involves investment techniques and risks different from those associated with ordinary mutual fund securities transactions and may involve increased transaction costs. The Fund’s investment in derivatives may rise or fall more rapidly in value than other investments and may reduce the Fund’s returns. Changes in the value of the derivative may not correlate perfectly, or at all, with the underlying asset, reference rate or index, and the Fund could lose more than the principal amount invested. Derivatives also may be subject to certain other risks such as leverage risk, liquidity risk, interest rate risk, market risk, credit risk, management risk and the risk of mispricing or improper valuation. Derivatives also may not behave as anticipated by the Fund’s, especially in abnormal market conditions. The use of derivatives may increase the volatility of the Fund’s net asset value. Derivatives may be leveraged such that a small investment in derivative securities can have a significant impact on the Fund’s exposure to stock market values, interest rates, currency exchange rates or other investments. As a result, a relatively small price movement in a derivatives contract may cause an immediate and substantial loss or gain. It may be difficult or impossible for the Fund to purchase or sell certain derivatives in sufficient amounts to achieve the desired level of exposure, which may result in a loss or may be costly to the Fund. In addition, the possible lack of a liquid secondary market for certain derivatives and the resulting inability of the Fund to sell or otherwise close out a derivatives position could expose the Fund to losses and could make such derivatives more difficult for the Fund to value accurately. Some derivatives are more sensitive to market price fluctuations and to interest rate changes than other investments. The Fund also could suffer losses related to its derivatives positions as a result of unanticipated market movements, which losses are potentially unlimited. The Fund also may be exposed to losses if the counterparty in the transaction does not fulfill its contractual obligation. In addition, derivatives traded over-the-counter (“OTC derivatives”) do not benefit from the protections provided by exchanges in the event that a counterparty is unable to fulfill its contractual obligation. Such OTC derivatives therefore involve greater counterparty and credit risk and may be more difficult to value than exchange-traded derivatives. When a derivative is used as a hedge against a position that the Fund holds, any loss generated by the derivative should generally be offset by gains on the hedged instrument, and vice versa. While hedging can reduce or eliminate losses, it also can reduce or eliminate gains. Hedges are sometimes subject to imperfect matching between the derivative and the hedged investment, and there can be no assurance that the Fund’s hedging transactions will be effective. Also, suitable derivative transactions may not be available in all circumstances. Derivatives are subject to fees and other costs which are not reflected in the Annual Fund Operating Expenses table.

Emerging Markets Risk. Foreign investment risk is typically magnified in emerging markets, which are the less developed and developing nations. Certain of these countries have in the past failed to recognize private property rights and have at times nationalized and expropriated the assets of private companies. Political, social and economic structures in many emerging market countries may be less established than in developed countries and may change rapidly. Such countries may also lack the social, political and economic characteristics of more developed countries. Unanticipated political, social or economic developments may affect the values of the Fund’s investments in emerging market countries and the availability to the Fund of additional investments in these countries.

The currencies of certain emerging market countries have from time to time experienced a steady devaluation relative to the U.S. dollar, and continued devaluations may adversely affect the value of the Fund’s assets denominated in such currencies. Many emerging market countries have experienced substantial rates of inflation for many years, and continued inflation may adversely affect the economies and securities markets of such countries.

The small size, limited trading volume and relative inexperience of the financial markets in these countries may make the Fund’s investments in such countries illiquid and more volatile than investments in more developed countries. There may be little financial or accounting information available with respect to issuers located in these countries, and it may be difficult as a result to assess the value or prospects of an investment in such issuers.

The system of share registration and custody in some emerging market countries may create certain risks of loss (including in some cases the risk of total loss) and the Fund may be required to establish special custodial or other arrangements before making investments in these countries. There is an increased risk of uninsured loss due to lost, stolen or counterfeit stock certificates or unauthorized trading, or other fraudulent activity.

Prior governmental approval of non-U.S. investments may be required and foreign investment in U.S. companies may be subject to limitation in some emerging market countries. Foreign ownership limitations also may be imposed by the charters of individual companies in emerging market countries to prevent, among other concerns, violation of foreign investment limitations. Repatriation of investment income, capital and proceeds of sales by foreign investors may require governmental registration and/or approval in some developing countries. The Fund could be adversely affected by delays in or a refusal to grant any required governmental registration or approval for such repatriation.

Risks of Investing in Russia. The United States and European Union have instituted various sanctions against certain Russian officials. These sanctions and other intergovernmental actions that may be undertaken against Russia may result in the devaluation of Russian currency, a downgrade in the country’s credit rating, and a decline in the value and liquidity of Russian stocks. These sanctions could result in the immediate freeze of Russian securities, impairing the ability of the Fund to buy, sell, receive or deliver those securities. In addition, retaliatory action by the Russian government could involve the seizure of assets and any such actions are likely to impair the value and liquidity of such assets. Any or all of these potential results could harm Russia’s economy. These sanctions, and the continued disruption of the Russian economy, could have a negative effect on the performance of the Fund.

and SZSE has historically not been permitted, other than through a license granted under regulations in the People’s Republic of China known as the Qualified Foreign Institutional Investor and Renminbi Qualified Foreign Institutional Investor systems. Each license permits investment in A-shares only up to a specified quota.

Investment in eligible A-shares through Stock Connect is subject to trading, clearance and settlement procedures that could pose risks to the Fund. Stock Connect imposes daily quota limitations, and investors may not purchase and sell the same security on the same trading day, which may restrict the Fund’s ability to enter into or exit trades on a timely basis. Stock Connect can operate only when the Shanghai or Shenzhen markets, in addition to the Hong Kong market, are open for trading and when banking services are available in both markets on the corresponding settlement days. As such, if one or both markets are closed on a U.S. trading day, the Fund may not be able to dispose of its A-shares in a timely manner, which could adversely affect Fund performance. HKEX, SSE, and SZSE each reserve the right to suspend trading and the A-shares market has historically had a higher propensity for trading suspensions than many other global equity markets. Because of the way in which A-shares are held in Stock Connect, the Fund may not be able to exercise the rights of a shareholder and may be limited in their ability to pursue claims against the issuer of a security.

The regulations of Stock Connect are relatively new and untested and are subject to changes, which could adversely impact the Fund’s rights with respect to its A-shares. As Stock Connect is relatively new, there are no assurances that the operational systems of the relevant market participants comprising the Stock Connect program will function properly, independently or in coordination with other participants.

limits on repatriation, adverse changes in investment or exchange control regulations, political instability, restrictions on the flow of international capital, imposition of foreign withholding or other taxes, fluctuating currencies, inflation, difficulty in obtaining and enforcing judgments against foreign entities or other adverse political, social or diplomatic developments that could affect the Fund’s investments. Foreign investments may be less liquid and their prices more volatile than the securities of U.S. companies. In addition, the time period for settlement of transactions in certain foreign markets generally is longer than for U.S. markets. Foreign investments may be denominated in currencies other than the U.S. dollar. Therefore, changes in foreign exchange rates will affect the value of the Fund’s foreign investments either beneficially or adversely. Fluctuations in foreign currency exchange rates will also affect the dollar value of dividends and interest earned, gains and losses realized on the sale of securities and net investment income and gains, if any, available for distribution to shareholders.

Geopolitical Risk. Geopolitical and other events may disrupt securities markets and adversely affect global economies and markets and thereby decrease the value of the Fund’s investments. War, terrorism, economic uncertainty, and related geopolitical events have led, and in the future may lead, to increased short-term market volatility and may have adverse long-term effects on U.S. and world economies and markets generally. Likewise, natural and environmental disasters, such as the earthquake and tsunami in Japan in early 2011, and systemic market dislocations of the kind surrounding the insolvency of Lehman Brothers in 2008, if repeated, would be highly disruptive to economies and markets, adversely affecting individual companies and industries, securities markets, interest rates, credit ratings, inflation, investor sentiment, and other factors affecting the value of the Fund’s investments. In January 2020, the United Kingdom (the “UK”) withdrew from the European Union (the “EU”), commonly referred to as “Brexit.” Uncertainty surrounding the withdrawal process and the consequences of Brexit could result in economic, market, and currency instability and volatility in the UK, Europe and worldwide. Additional members of the EU could pursue similar procedures to withdraw from the EU, increasing the risk of such instability and volatility.

During global market disruptions, the Fund’s exposure to the risks described elsewhere in this Prospectus will likely increase. Market disruptions can also prevent the Fund from implementing its investment strategies for a period of time and achieving its investment objective. For example, a market disruption may adversely affect the orderly functioning of the securities markets and may cause the Fund’s derivatives counterparties to discontinue offering derivatives on some underlying securities, reference rates, or indices, or to offer them on a more limited basis.

Interest Rate Risk. Normally, the values of fixed income securities vary inversely with changes in prevailing interest rates. The value of the Fund’s fixed income securities tends to decrease when interest rates rise and tends to increase when interest rates fall. Securities with longer maturities or durations held by the Fund are generally more sensitive to interest rate changes. As such, securities with longer maturities or durations are usually more volatile than those with shorter maturities or durations. The Fund’s investment in variable rate securities will generally be less sensitive to interest rate changes, but such securities may decline in value if their interest rates do not rise as much, or as quickly, as interest rates in general. The negative impact on fixed income securities from rising interest rates could be swift and significant and negatively impact the Fund’s net asset value.

results from increases in the value of the security, such losses are theoretically unlimited. An investment in an inverse ETF could result in a loss of the entire investment in that particular ETF. To the extent the inverse ETF uses derivatives to achieve short exposure, it is subject to derivatives risk including the risk of leverage.

Leverage Risk. The Fund’s investments in derivatives or exposure to derivatives through other investment vehicles expose the Fund to leverage inherent in such instruments. Such leveraged investments can amplify the effects of market volatility on the Fund’s net asset value (i.e., relatively small market movements may result in large changes in the Fund’s net asset value) and make the Fund’s returns more volatile. At times, the Fund’s leveraged investments may cause the Fund’s investment exposure to exceed its net assets and could cause the Fund to experience substantial losses, including the risk of total loss, if the market moves against the Fund. The use of leveraged investments may also cause the Fund to liquidate portfolio positions when it would not be advantageous to do so in order to satisfy its obligations or to meet asset segregation requirements. The use of leveraged investments may also cause the Fund to have higher expenses than those of mutual funds that do not use such techniques.

LIBOR Transition Risk. Certain instruments in which the Fund may invest rely in some fashion upon the London Interbank Offered Rate (LIBOR). The United Kingdom’s Financial Conduct Authority, which regulates LIBOR, has announced plans to phase out the use of LIBOR by the end of 2021. There remains uncertainty regarding the future utilization of LIBOR and the nature of any replacement rate, and any potential effects of the transition away from LIBOR on the Fund or on certain instruments in which the Fund invests are not known. The transition process may involve, among other things, increased volatility or illiquidity in markets for instruments that currently rely on LIBOR. The transition may also result in a reduction in the value of certain instruments held by the Fund or reduce the effectiveness of related Fund transactions such as hedges. Any such effects of the transition away from LIBOR, as well as other unforeseen effects, could result in losses to the Fund.

Liquidity Risk. Investments that trade less frequently can be more difficult or more costly to buy, or to sell, than more liquid or active investments. It may not be possible to sell or otherwise dispose of illiquid securities both at the price and within a time period deemed desirable by the Fund. Securities subject to liquidity risk in which the Fund may invest include emerging markets securities, private placements, Rule 144A securities, below-investment-grade securities, securities of small companies and other securities without an established market. Liquidity risk may be magnified for fixed income securities in a rising interest rate environment if there is increased supply in the market due to selling activity. If dealer capacity in fixed income markets is insufficient for market conditions, it may further inhibit liquidity and increase volatility in the fixed income markets.

Market Risk. The value of the Fund’s investments may go up or down, sometimes rapidly or unpredictably. The value of an investment may decline due to factors affecting securities markets generally or particular industries represented in the securities markets. The value of an investment may decline due to general market conditions that are not specifically related to a particular company, such as real or perceived adverse economic conditions, changes in the general outlook for corporate earnings, changes in interest or currency rates or adverse investor sentiment generally. Furthermore, local, regional and global events such as war, acts of terrorism, social unrest, natural disasters, the spread of infectious illness or other public health threats could also adversely impact issuers, markets and economies, including in ways that cannot necessarily be foreseen. The Fund could be negatively impacted if the value of a portfolio holding were harmed by such political or economic conditions or events. The value of an investment may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously.

Mortgage-Backed/Asset-Backed Securities Risk. The value of the Fund’s mortgage-backed or asset-backed securities may be affected by, among other things, changes in interest rates, factors concerning the interests in and structure of the issuer or the originator of the mortgages, the creditworthiness of the entities that provide any supporting letters of credit, surety bonds or other credit enhancements or the market’s assessment of the quality of underlying assets. During periods of rising interest rates, property owners may prepay their mortgages more

slowly than expected, resulting in slower prepayments of mortgage-backed securities, which increases the duration of a security and may reduce its value. When interest rates decline, property owners may prepay their mortgages more quickly than expected. This can reduce the returns of the Fund because the Fund may have to reinvest that money at the lower prevailing interest rates. The Fund’s investments in other asset-backed securities are subject to similar extension and prepayment risks as those described above for mortgage-backed securities.

Mortgage-Backed To-Be-Announced (TBA) Securities Risk. To the extent the Fund purchases or sells mortgage-backed to-be-announced (TBA) securities, the Fund is subject to the risk that the counterparty may fail to consummate the transaction, which could cause the Fund to miss the opportunity to obtain a price or yield considered to be advantageous. Mortgage-backed TBAs may also have a leverage-like effect on the Fund and may cause the Fund to be more volatile. To the extent the Fund “rolls over” mortgage-backed TBA agreements prior to the settlement date, the Fund may experience higher portfolio turnover and increased taxable gains.

Operational and Technology Risk. Cyber-attacks, disruptions, or failures that affect the Fund’s service providers or counterparties, issuers of securities held by the Fund, or other market participants may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Cyber-attacks may include unauthorized attempts by third parties to improperly access, modify, disrupt the operations of, or prevent access to the systems of the Fund’s service providers or counterparties, issuers of securities held by the Fund or other market participants or data within them. In addition, power or communications outages, acts of god, information technology equipment malfunctions, operational errors, and inaccuracies within software or data processing systems may also disrupt business operations or impact critical data. Market events also may trigger a volume of transactions that overloads current information technology and communication systems and processes, impacting the ability to conduct the Fund’s operations.

Cyber-attacks, disruptions, or failures may adversely affect the Fund and its shareholders or cause reputational damage and subject the Fund to regulatory fines, litigation costs, penalties or financial losses, reimbursement or other compensation costs, and/or additional compliance costs. For example, the Fund’s or its service providers’ assets or sensitive or confidential information may be misappropriated, data may be corrupted, and operations may be disrupted (e.g., cyber-attacks or operational failures may cause the release of private shareholder information or confidential Fund information, interfere with the processing of shareholder transactions, impact the ability to calculate the Fund’s net asset value (“NAV”), and impede trading). In addition, cyber-attacks, disruptions, or failures involving the Fund counterparty could affect such counterparty’s ability to meet its obligations to the Fund, which may result in losses to the Fund and its shareholders. Similar types of operational and technology risks are also present for issuers of securities held by the Fund, which could have material adverse consequences for such issuers, and may cause the Fund’s investments to lose value. Furthermore, as a result of cyber-attacks, disruptions, or failures, an exchange or market may close or issue trading halts on specific securities or the entire market, which may result in the Fund being, among other things, unable to buy or sell certain securities or financial instruments or unable to accurately price its investments.

While the Fund and its service providers may establish business continuity and other plans and processes that seek to address the possibility of and fallout from cyberattacks, disruptions, or failures, there are inherent limitations in such plans and systems, including that they do not apply to third parties, such as Fund counterparties, issuers of securities held by the Fund, or other market participants, as well as the possibility that certain risks have not been identified or that unknown threats may emerge in the future and there is no assurance that such plans and processes will address the possibility of and fallout from cyber-attacks, disruptions, or

failures. In addition, the Fund cannot directly control any cybersecurity plans and systems put in place by its service providers, Fund counterparties, issuers of securities held by the Fund, or other market participants.

Regulatory Risk. Future regulatory developments could impact the Fund’s ability to invest in certain derivatives. It is possible that government regulation of various types of derivative instruments, including futures, options and swap agreements, may limit or prevent the Fund from using such instruments as a part of its investment strategies, and could ultimately prevent the Fund from being able to achieve its investment objective. In December 2015, the SEC proposed a new rule to regulate the use of derivatives by registered investment companies, such as the Fund. If the rule goes into effect as proposed, it could affect the Fund’s investments in derivatives. It is impossible to fully predict the effects of past, present or future legislation and regulation in this area, but the effects could be substantial and adverse. It is possible that legislative and regulatory activity could limit or restrict the ability of the Fund to use certain derivatives as a part of its investment strategies and could alter, perhaps to a material extent, the nature of an investment in the Fund or the ability of the Fund to continue to implement its investment strategies.

The futures, options and swaps markets are subject to comprehensive statutes, regulations, and margin requirements. In addition, the SEC, Commodity Futures Trading Commission (“CFTC”) and the exchanges are authorized to take extraordinary actions in the event of a market emergency, including, for example, the implementation or reduction of speculative position limits, the implementation of higher margin requirements, the establishment of daily price limits and the suspension of trading. The regulation of futures, options and swaps transactions in the United States is a changing area of law and is subject to modification by government and judicial action.

In particular, the Dodd-Frank Wall Street Reform and Consumer Protection Act (the “Dodd-Frank Act”) was signed into law on July 21, 2010. The Dodd-Frank Act has changed the way in which the U.S. financial system is supervised and regulated. Title VII of the Dodd-Frank Act sets forth a legislative framework for OTC derivatives, including financial instruments, such as swaps, in which the Fund may invest. Title VII of the Dodd-Frank Act made broad changes to the OTC derivatives market, grants significant authority to the SEC, the CFTC, and other federal regulators to regulate OTC derivatives and market participants, and requires clearing and exchange trading of many OTC derivatives transactions. The CFTC and the SEC finalized the definition of “swap” and “security-based swap” and provided parameters around which contracts will be subject to further regulation under the Dodd-Frank Act. Provisions in the Dodd-Frank Act include new capital and margin requirements and the mandatory use of clearinghouse mechanisms for many OTC derivative transactions. The CFTC, SEC and other federal regulators have been tasked with developing the rules and regulations enacting the provisions of the Dodd-Frank Act. While certain of the rules are now effective, other rules are not yet final, so it is not possible at this time to gauge the exact nature and scope of the impact of the Dodd-Frank Act on the Fund. Since 2010, and most notably in 2015 and 2016, comprehensive legislation has been proposed that is intended to pare back some of the provisions of the Dodd-Frank Act.

In November 2019, the SEC published a proposed rulemaking related to the use of derivatives and certain other transactions by registered investment companies that would, if adopted, for the most part rescind the guidance of the SEC and its staff regarding asset segregation and cover transactions. Instead of complying with current guidance, the Fund would need to trade derivatives and other transactions that create future payment or delivery obligations (except reverse repurchase agreements and similar financing transactions) subject to a value-at-risk (“VaR”) leverage limit, certain other derivatives risk management program and testing requirements and requirements related to board and SEC reporting. These new requirements would apply unless the Fund qualified as a “limited derivatives user,” as defined in the SEC’s proposal. Any new requirements, if adopted, may increase the cost of the Fund’s investments and cost of doing business, which could adversely affect investors.

The Adviser is registered with the National Futures Association as a “commodity pool operator” and the Adviser will act as such with respect to the operation of the Fund and its Subsidiary as a result of CFTC regulations. As a result, the Adviser and the Fund are subject to dual regulation by the CFTC and the SEC. The CFTC adopted regulations that seek to “harmonize” CFTC regulations with overlapping SEC rules and regulations. The Adviser has availed itself of the CFTC’s substitute compliance option under the harmonization regulations with respect to the Fund by filing a notice with the National Futures Association. The Fund and the Adviser will remain subject to certain CFTC-mandated disclosure, reporting and recordkeeping regulations. Compliance with the CFTC regulations could increase the Fund’s expenses, adversely affecting investment returns.

time, the Fund may invest in the equity securities of very small cap companies, often referred to as “micro-cap” companies. For purposes of the Fund, “micro-cap” companies are those with market capitalizations of $500 million or less at the time of the Fund’s investment. The considerations noted above are generally intensified for these investments.

Subsidiary Risk. The Subsidiary is not registered under the Investment Company Act of 1940, as amended (the “1940 Act”) and is not subject to the investor protections of the 1940 Act. By investing in the Subsidiary, the Fund is exposed to the risks associated with the Subsidiary’s investments. Changes in the laws of the United States and/or the Cayman Islands could result in the inability of the Fund and/or the Subsidiary to operate as described in the Prospectus and could adversely affect the Fund.

Tax Risk. In order for the Fund to qualify as a regulated investment company under Subchapter M of the Code, the Fund must derive at least 90% of its gross income each taxable year from certain qualifying sources of income (“qualifying income”). The Fund’s intention to qualify as a regulated investment company may limit its ability to make certain investments including, without limitation, investments in certain commodity-linked derivatives, since income from commodity-linked derivatives may not constitute qualifying income to the Fund. Receipt of such income could cause the Fund to fail to qualify as a regulated investment company and be subject to U.S. federal income tax on its taxable income at corporate rates. The Fund also may incur transaction and other costs to comply with any new or additional guidance from the IRS. The IRS has issued regulations that generally treat the Fund’s income inclusion with respect to the Subsidiary as qualifying income if there is a distribution in the same taxable year out of the earnings and profits of the Subsidiary that is attributable to such income inclusion, or if the Fund’s income inclusion with respect to the Subsidiary is derived in connection with the Fund’s business of investing in stocks, securities, or currencies. The tax treatment of commodity-linked derivatives and income from the Subsidiary also may be adversely affected by future legislation, Treasury Regulations and/or guidance issued by the IRS that could affect the character, timing and/or amount of the Fund’s taxable income or any gains and distributions made by the Fund.

Trustees, Officers and Adviser. The Board of Trustees of the William Blair Funds (the “Trust”) has overall management responsibility. The duties of the trustees and officers of the Trust include overseeing the business affairs of the Trust, monitoring investment activities and practices and considering other matters concerning the Trust. The Statement of Additional Information has the names of and additional information about the trustees and officers of the Trust. Subject to the oversight of the Board of Trustees, William Blair Investment Management, LLC (the “Adviser” or “WBIM”), 150 North Riverside Plaza, Chicago, Illinois 60606, is responsible for providing investment advisory and management services to the Fund, including making decisions regarding Fund portfolio transactions, pursuant to a management agreement (the “Management Agreement”). The Statement of Additional Information includes information on brokerage commissions paid by the Fund in 2019, including any amounts directed to third parties to pay for third party research. William Blair & Company, L.L.C. is the principal underwriter and distributor of the Trust and acts as agent of the Trust in the sale of its shares (the “Distributor” or “WBC”). WBIM and WBC are collectively referred to herein as “William Blair.”

For the fiscal year ended December 31, 2019, the Fund was contractually obligated to pay the Adviser a management fee of 0.80% of the Fund’s average daily net assets.

The Adviser has entered into a contractual agreement with the Fund to waive fees and/or reimburse expenses, if necessary, in order to limit the Fund’s operating expenses (excluding interest expenses, taxes, brokerage commissions, acquired fund fees and expenses, dividend and interest expenses on short sales, other investment-related costs and extraordinary expenses, such as litigation and other expenses not incurred in the ordinary course of the Fund’s business) for each class to the level reflected in the table below until April 30, 2021. The agreement terminates upon the earlier of April 30, 2021 or the termination of the Management Agreement.

Because of the expense limitation agreement, the Fund may pay the Adviser less than the contractual management fee.

Additional Information. The Trust enters into contractual arrangements with various parties, including, among others, the Fund’s investment adviser, custodian, transfer agent, accountants and distributor, who provide services to the Fund. Shareholders are not parties to, or intended (or “third-party”) beneficiaries of, any of those contractual arrangements, and those contractual arrangements are not intended to create in any individual shareholder or group of shareholders any right to enforce the terms of the contractual arrangements against the service providers or to seek any remedy under the contractual arrangements against the service providers, either directly or on behalf of the Trust.

This Prospectus provides information concerning the Trust and the Fund that you should consider in determining whether to purchase shares of the Fund. The Fund may make changes to this information from time to time. Neither this Prospectus, the SAI or any document filed as an exhibit to the Trust’s registration statement, is intended to, nor does it, give rise to an agreement or contract between the Trust or the Fund and any shareholder, or give rise to any contract or other rights in any individual shareholder, group of shareholders or other person other than any rights conferred explicitly by federal or state securities laws that may not be waived.

Portfolio Management. Additional information is provided below on the Fund’s portfolio managers. The Statement of Additional Information provides additional information about the portfolio managers including the structure of their compensation, other accounts they manage and their ownership of securities in the Fund.

The Fund is co-managed by Brian D. Singer and Thomas Clarke. Messrs. Singer and Clarke are responsible for investment strategy, asset and currency allocation, and portfolio construction.

Brian D. Singer, a Partner of William Blair Investment Management, LLC, has co-managed the Fund since its inception in 2011. He joined William Blair in 2011. Prior to joining William Blair, he was a Managing Partner and Head of Investment Strategies at Singer Partners, LLC from 2009 to 2011. Prior to that, he was the head of the UBS Global Investment Solutions Group and Americas’ Chief Investment Officer, UBS Global Asset Management (Americas) Inc., from 2003 to 2007. He serves on the Exeter College at Oxford University Endowment Investment Committee and is a member of the Free To Choose Network board, which is inspired by the ideas of economist Milton Friedman. He holds the Chartered Financial Analyst designation and is a member of the CFA Institute. Education: B.A., Economics, Northwestern University; M.B.A., University of Chicago.

Thomas Clarke, a Partner of William Blair Investment Management, LLC, has co-managed the Fund since its inception in 2011. He joined William Blair in 2011. Prior to joining William Blair, he was a Managing Partner at Singer Partners, LLC from 2009 to 2011. Prior to that, he was with UBS Global Asset Management (Americas) Inc. from 2000 to 2009. During his time at UBS Global Asset Management (Americas) Inc., he served as the head of currency analysis and strategy for the UBS Global Investment Solutions Group from 2000 to 2009. Before joining UBS in 2000, he was head of currency for Rothschild Asset Management, where he spent 10 years as a part of the fixed income and currency group. Education: BSc, University of Manchester (UK).

Custodian. The Custodian for the Fund is State Street Bank and Trust Company, State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111. The Custodian is responsible for custody of portfolio securities, fund accounting and the calculation of the Fund’s net asset value.

Transfer Agent and Dividend Paying Agent. The Transfer Agent and Dividend Paying Agent is DST Asset Manager Solutions, Inc. (“DST”), 2000 Crown Colony Drive, Quincy, Massachusetts 02169-0953.

Class I shares are available for purchase by the following categories of investors who meet the minimum investment requirements (except as noted):

To the extent a shareholder or group of shareholders (either directly or through an intermediary) are not listed in the above categories but they held Class I shares of the Fund prior to May 1, 2019, such investors are entitled to continue to invest in Class I shares of the Fund.

William Blair may make certain additional exceptions to these requirements, which are discussed below. The Fund will consider requests by holders of Class N shares to convert such shares to Class I shares on a case by case basis, provided eligibility requirements and relevant minimums are met.

Class R6 shares are offered to the following investors, provided that neither these investors nor their intermediaries require the Fund to make any type of servicing or administrative payments with respect to Class R6 shares:

Class R6 shares are not available to retail taxable or tax-advantaged accounts seeking to invest directly in the Fund outside of an omnibus account maintained by an intermediary, except as noted above. To the extent a shareholder or group of shareholders (either directly or through an intermediary) are not listed in the above categories but they held Institutional Class shares of the Fund prior to May 1, 2019, such investors are entitled to continue to invest in Class R6 shares of the Fund. The Fund will consider requests by holders of Class I shares to convert such shares to Class R6 shares on a case by case basis, provided eligibility requirements and relevant minimums are met.

Minimum Investments. The minimum initial investment for an account is $1 million (or any lesser amount if, in William Blair’s opinion, the investor has adequate intent and availability of funds to reach a future level of investment of $1 million). There is no minimum for subsequent purchases.

Share Class Minimum Maintenance. If an account’s balance falls below the minimum initial investment amount for that share class due to account redemptions (and not due to market depreciation), the Fund reserves the right to convert or redeem shares held by the account in the following manner:

The applicable shareholder or intermediary will be notified prior to any such redemption or conversion and will be allowed 60 days to make additional investments and bring the account into compliance with the applicable investment minimum before any conversion or redemption occurs. Any conversion will occur at the relative NAV of the two applicable share classes at the time of conversion and the account value will not change as a result of the conversion, although the number of shares held may change.

A conversion between share classes of the Fund is generally not a taxable event. Please consult your tax advisor for an assessment of the tax implications of any conversion.

ADDITIONAL INFORMATION AND EXCEPTIONS TO ELIGIBILITY AND MINIMUM INVESTMENT REQUIREMENTS FOR CLASS N, CLASS I AND CLASS R6 SHARES

The Distributor may, in its sole discretion, reject any purchase order from the shareholder and/or intermediary involved.

Distribution Agreement. The Trust has adopted a plan under Rule 12b-1 of the 1940 Act, that applies only to Class N shares that provides for a fee at the annual rate of 0.25% of the Fund’s average daily net assets attributable to Class N shares for distribution and other services provided to shareholders of Class N. Because 12b-1 fees are paid out of Fund assets on an ongoing basis, they will, over time, increase the cost of investment

in Class N shares and may cost more than other types of sales charges. As a result, long-term shareholders may pay more than the economic equivalent of the maximum initial sales charge permitted by FINRA.

Other Payments. Class N and Class I shares of the Fund may reimburse William Blair for fees paid on the Fund’s behalf to intermediaries such as banks, broker-dealers, financial advisers or other financial institutions for sub-administration, sub-transfer agency and other services provided to shareholders whose shares are held of record in omnibus, other group accounts, retirement plans or accounts traded through registered securities clearing agents. These fees may be based on the number of subaccounts serviced or based on average net assets held in the Fund for Class N and Class I shares.

William Blair, out of its own resources and without additional cost to the Fund or its shareholders, provides additional cash payments to certain intermediaries (which may be referred to as revenue sharing). Such payments to intermediaries are in addition to distribution fees, or fees paid for sub-administration, sub-transfer agency or other services by the Fund for Class N and Class I shares. William Blair may pay firms for administrative, sub-accounting, or shareholder processing services and/or for providing Class N, Class I or Class R6 shares of the Fund with “shelf space” or access to a third party platform, inclusion of Class N, Class I or Class R6 shares of the Fund on preferred or recommended sales lists, mutual fund “supermarket” platforms and other sales programs, allowing William Blair access to an intermediary’s conferences and meetings and other forms of marketing support. The level of payments made may be a fixed fee or based on one or more of the following factors: current assets, number of accounts and/or number of transactions for Class N, Class I or Class R6 shares attributable to the intermediary or fund type or other measure agreed to by William Blair and the intermediary. The amount of payments is different for different intermediaries.

The Distributor currently makes payments to intermediaries in amounts that generally range from 0.01% to 0.15% of the assets of the Fund’s shares that are serviced and maintained by the intermediary. These amounts are subject to change. Receipt of, or the prospect of receiving, this compensation may influence the intermediary’s recommendation of the Fund or availability of the Fund through the intermediary. Further information on payments to third parties is included in the Statement of Additional Information.

The information below relating to buying, selling and exchanging shares of the Fund applies if you are transacting directly with the Fund. Shares of the Fund are also available through certain financial intermediaries, such as a bank or a broker-dealer (each, an “intermediary”). If you are investing through an intermediary, you are not placing your orders directly with the Fund, and you must follow the intermediary’s transaction procedures. Your intermediary may impose different or additional conditions than the Fund on purchases, redemptions and exchanges of Fund shares. These differences may include different minimum initial (and subsequent) investment amounts, exchange policies, fund choices, cut-off times for investment and other trading restrictions. Your intermediary also may impose charges for its services in addition to the fees charged by the Fund. You should consult with your intermediary directly for information regarding its conditions and fees for buying, selling or exchanging shares of the Fund. The Fund is not responsible for the failure of your intermediary to carry out its responsibilities.

Purchase Price. The Fund is sold at its public offering price, which is the net asset value per share that is next computed after receipt of your order in proper form by the Distributor, the Transfer Agent or a designated agent thereof. (For more information, see “Determination of Net Asset Value.”) If you fail to pay for your order, you will be liable for any loss to the Fund and, if you are a current shareholder, the Fund may redeem some or all of your shares to cover such loss.

Note: All purchases made by check should be in U.S. dollars and made payable to William Blair Funds, or in the case of a retirement account, the custodian or trustee of such account. Third party checks generally will not be accepted. When purchases are made by check or periodic account investment, the Fund may delay sending redemption proceeds until it determines that collected funds have been received for the purchase of such shares, which may be up to 15 calendar days.

Purchase in Kind. You may, subject to the approval of the Fund, purchase shares of the Fund with securities that are eligible for purchase by the Fund (consistent with the Fund’s investment process, goal and philosophy) and that have values that are readily ascertainable in accordance with the Fund’s valuation policies. Call the Fund at 1-800-742-7272 if you would like to purchase shares of the Fund with other securities. Such purchases may result in the recognition of gain or loss for federal income tax purposes on the securities transferred to the Fund.

Right to Reject Your Purchase Order. The Trust is required to obtain, verify and record certain information regarding the identity of shareholders. When opening a new account, the Trust will ask for your name, address, taxpayer identification number, date of birth and other information that identifies you. You may also be asked to show identifying documents. Applications without this information may not be accepted and orders may not be processed. The Trust reserves the right to place limits on transactions in any account until the identity of the investor is verified; refuse an investment in the Fund or involuntarily redeem an investor’s shares and close an account in the event that an investor’s identity is not verified; or suspend the payment of withdrawal proceeds if it is deemed necessary to comply with anti-money laundering regulations. The Trust and its agents will not be responsible for any loss resulting from an investor’s delay in providing all required identifying information or from closing an account and redeeming an investor’s shares when an investor’s identity cannot be verified.

Short-Term and Excessive Trading. The Fund is designed for long-term investors. The Fund discourages and does not accommodate short-term or excessive trading. Such trading may present risks to other shareholders in the Fund, including disruption of portfolio investment strategies, with potential resulting harm to performance, and increased trading costs or Fund expenses. Thus, such trading may negatively impact the Fund’s net asset value and result in dilution to long-term shareholders. Short-term and excessive trading in Fund shares can also negatively impact the Fund’s long-term performance by requiring the Fund to maintain more assets in cash or to liquidate holdings at a disadvantageous time. These risks may be more pronounced for the Fund because of its investment in securities that are susceptible to pricing arbitrage (e.g., international securities, emerging markets securities and small cap securities).

In an effort to protect long-term shareholders, the Board of Trustees has adopted policies and procedures that seek to deter short-term and excessive trading and to detect such trading activity at levels that may be detrimental to the Fund. The Fund reserves the right to reject or restrict any purchase order (including exchanges) from any investor for any reason, including excessive, short-term or other abusive trading practices that may disrupt portfolio management strategies and harm Fund performance. The Fund also reserves the right to delay delivery of redemption proceeds up to seven days or to honor certain redemptions with securities, rather than cash.

In making the determination to exercise these rights, the Fund may consider an investor’s trading history in the Fund and accounts under common ownership or control. The Fund seeks to employ reasonable measures to detect short-term and excessive trading at levels that may be detrimental to the Fund. Accordingly, the Adviser uses certain materiality and volume thresholds to detect short-term or excessive trading, but otherwise seeks to apply the policies uniformly to all shareholders, as described in more detail below.

Some Fund shares are held through omnibus account arrangements, whereby a broker-dealer, investment adviser, retirement plan sponsor or other financial intermediary maintains an omnibus account with the Fund for trading on behalf of its customers. For such accounts, the Adviser generally seeks to monitor trading activity at the omnibus level in an attempt to identify disruptive trades using certain thresholds. However, shareholders seeking to engage in short-term or excessive trading may use a variety of strategies to avoid detection and, despite the efforts of the Fund and its agents to prevent short-term or excessive trading, there is no guarantee that the Fund or its agents will be able to identify such shareholders or curtail their trading practices. Also, the ability of the Fund and its agents to detect and curtail short-term and excessive trading practices may be limited by operational systems and technological limitations. In addition, the Fund receives purchase, exchange and redemption orders through financial intermediaries and cannot always know or reasonably detect short-term or excessive trading that may be facilitated by these intermediaries or by the use of omnibus account arrangements.

Under agreements that the Fund has entered into with intermediaries, the Fund may request transaction information from intermediaries at any time to determine whether there has been short-term trading by the intermediaries’ customers. The Fund will request that the intermediary provide individual account level detail (or participant level detail in the case of retirement plans) to the Fund at its request. If short-term trading is detected at the individual account or participant level, the Fund will request that the intermediary a) continue to monitor the individual or participant, b) issue the individual or participant a warning, or c) ban the individual or participant from making further purchases of Fund shares. An intermediary may apply its own short-term trading policies and procedures, which may be more or less restrictive than the Fund’s policies and procedures. There is no assurance that the Fund’s policies will be effective in limiting and deterring short-term and excessive trading in all circumstances.

Opening an Account—Class N shares and Class I shares. To open a new account for Class N shares or Class I shares of the Fund by mail, make out a check for the amount of your investment, payable to “William Blair Funds.” Complete the account application included with this Prospectus and mail the completed application and the check to the Transfer Agent, DST Asset Manager Solutions, Inc., P.O. Box 219137, Kansas City, Missouri 64121-9137.

Adding to an Account—Class N shares and Class I shares. To purchase additional Class N shares or Class I shares, make out a check for the amount of your investment, payable to “William Blair Funds” and mail the check, together with a letter that specifies the Fund name, the account number and the name(s) in which the account is registered to DST Asset Manager Solutions, Inc., P.O. Box 219137, Kansas City, Missouri 64121-9137.

Opening or Adding to an Account—Class R6 shares. Opening a new account or adding to an account for Class R6 shares may only be done by wire. See “By Wire” below.

Adding to an Account—Class N shares and Class I shares. To add to your account by wire, instruct your bank to wire federal funds to:

Opening or Adding to an Account—Class R6 shares. First, call the Distributor at 1-800-742-7272 for an account number. Then instruct your bank to wire federal funds to:

Include the name of the Fund in which you are investing, your assigned account number and the name(s) in which the account is registered. Finally, complete the account application, indicate the account number assigned to you by the Distributor and mail it to the Distributor, William Blair & Company, L.L.C., 150 North Riverside Plaza, Chicago, Illinois 60606.

To redeem some or all of your shares by wire, you may contact DST, by mail or telephone, as explained herein. To redeem by wire, you must have elected this option on your account application and attached to the application, for Class N shares and Class I shares, a voided, unsigned check or deposit slip for your bank account, and for Class R6 shares, a corporate resolution authorizing those able to act on your behalf.

To redeem shares by telephone, you must have elected this option on your account application. Contact DST at 1-800-635-2886 (in Massachusetts, 1-800-635-2840).

Note: Telephone redemption requests should NOT be directed to the Trust or to the Distributor.

Signature guarantees, if required, must appear on the written redemption request and on any endorsed stock certificate or stock power.

Under normal conditions, the Fund typically expects to meet redemption requests through the use of the Fund’s holdings of cash or cash equivalents or by selling other Fund assets. A redemption in kind may be used as discussed below.

Redemptions In Kind. The Trust reserves the right to make redemption payments in whole or in part in securities or other financial assets, valued for this purpose as they are valued in computing the net asset value for the Fund’s shares. In making a redemption payment “in kind,” the Fund will typically distribute a pro rata portion of all securities or other financial assets, subject to certain exclusions approved by the Board of Trustees. Shareholders will receive cash for the portion of excluded securities and the Fund’s holdings of cash and receivables.

Shareholders receiving securities or other financial assets may realize a gain or loss for federal income tax purposes as a result of the redemption, and will incur any costs of sale, as well as the associated inconveniences. Notwithstanding the above, the Fund is obligated to redeem shares solely in cash up to the lesser of $250,000 or 1.00% of the net asset value of the Fund during any 90-day period for any one shareholder of record.

Subject to the following limitations, you may exchange Class N, Class I or Class R6 shares of a Fund for the same class of shares of another William Blair Fund at their relative net asset values so long as the shares to be acquired are available for sale in your state of residence and the other William Blair Fund is open to new investors. Exchanges into a closed Fund are precluded unless the shareholder already has an open account in that Fund. Exchanges will be effected by redeeming your shares and purchasing shares of the other William Blair Fund(s) requested. Shares of the Fund with a value in excess of $1 million acquired by exchange from another William Blair Fund may not be exchanged thereafter until they have been owned for 15 days (the “15 Day Hold Policy”). The Fund reserves the right to reject any exchange order for any reason, including excessive, short-term (market timing) or other abusive trading practices that may disrupt portfolio management. Exchanges will result in the recognition for federal income tax purposes of gain or loss on the shares exchanged. You should obtain and carefully read the prospectus of the William Blair Fund(s) you want to exchange into prior to making an exchange. You may obtain a prospectus by calling 1-800-635-2886 or by going to the Trust’s website at williamblairfunds.com.

Income Dividends. The Fund may earn dividends from stocks and interest from bond, money market and other investments, as well as net short-term capital gains from sales of securities, all of which are passed through to shareholders as income dividends as long as expenses do not exceed income.

Capital Gain Distributions. The Fund may realize capital gains whenever it sells securities for a higher price than it paid for them, which then will generally be passed through to shareholders as capital gain distributions to the extent that the Fund’s net long-term capital gains exceed the sum of its net short-term capital losses for such year and any capital loss carryovers available from prior years.

As a shareholder, you are entitled to your portion of the Fund’s net income and gains on its investments. The Fund passes its earnings along to you as dividends and distributions. The Fund’s policy is to distribute substantially all net investment income, if any, and all realized net capital gain, if any. All distributions of income and capital gain and any return of capital have the effect of immediately thereafter decreasing net asset value per share. Income dividends and capital gain distributions will be automatically reinvested in additional shares at net asset value on the reinvestment date, unless you specifically request otherwise (see “Shareholder Services and Account Policies—Dividend Options”). Cash payments are made by the Dividend Paying Agent shortly following the reinvestment date.

When Dividends are Paid. All income dividends, if any, and capital gain distributions, if any, generally will be paid annually in December and/or January. The Fund may vary these dividend practices at any time. Income dividends and any capital gain distributions made by the Fund will vary from year to year. Dividends and distributions may be subject to withholding, as required by the Internal Revenue Service (see “Your Account—Federal Income Taxes”).

As with any investment, you should consider how your investment in the Fund will be taxed. If your account is not a tax-advantaged account, the federal income tax implications of your investment in the Fund include the following:

Taxes on Distributions. The Fund’s distributions from current and accumulated earnings and profits are subject to federal income tax and may also be subject to state or local taxes. Distributions may be taxable at different tax rates depending upon the type of security and the length of time the Fund holds the security generating the income or gain that is distributed. Your distributions are generally taxable when they are paid, whether you take them in cash or reinvest them in additional shares. However, dividends declared in October, November or December to shareholders of record as of a date in one of those months and paid before the following February 1 are treated as having been paid on December 31 of the calendar year declared for federal income tax purposes. After the close of each calendar year, the Fund will inform you of the amount and nature of distributions paid.

long-term capital gains, provided the Fund and the shareholder each satisfy certain holding period and other requirements. Net capital gain distributions are taxed at long-term capital gain rates regardless of how long you have held your shares. A portion of the Fund’s dividends may be eligible for treatment as qualified dividend income.

Taxes on Transactions. Redemptions of Fund shares and exchanges for shares of other William Blair Funds are generally treated as a sale of such shares subject to federal income taxation and possibly state and local taxation. If the shares are held as a capital asset, then you will recognize, subject to the discussion below, a capital gain or loss measured by the difference between your basis in your shares and the price that you receive when you sell (or exchange) such shares. The capital gain or loss upon a sale, exchange or redemption of Fund shares will generally be a short-term capital gain or loss if such shares were held for one year or less, and will be a long-term capital gain or loss if such shares were held for more than one year. Long-term capital gains are generally taxable to individuals and other non-corporate shareholders at a maximum federal income tax rate of 20%. Any loss recognized on the redemption of shares held six months or less, however, will be treated as a long-term capital loss to the extent you have received any long-term capital gain dividends on such shares. If you realize a loss on the redemption or exchange of Fund shares and acquire within 30 days before or after such redemption or exchange shares of the Fund (including through reinvestment of dividends) or substantially identical stock or securities, the two transactions may be subject to the “wash sale” rules of the Code, resulting in a postponement of the recognition of such loss for federal income tax purposes. Capital losses may be subject to limitations on their use by a shareholder.

An additional 3.8% Medicare contribution tax is imposed on certain net investment income (including income dividends and capital gain distributions received from the Fund and net gains from redemptions or other taxable dispositions of Fund shares) of U.S. individuals, estates and trusts to the extent that such person’s “modified adjusted gross income” (in the case of an individual) or “adjusted gross income” (in the case of an estate or trust) exceeds a threshold amount.

Effect of Foreign Taxes. Investment income received from sources within foreign countries may be subject to foreign income and other taxes, which generally will reduce the Fund’s distributions. However, the United States has entered into tax treaties with many foreign countries that entitle certain investors to a reduced rate of tax or to certain exemptions from tax. Accordingly, the Fund will attempt to operate so as to qualify for such reduced tax rates or tax exemptions whenever practicable.

“Buying a Dividend.” If you buy shares before the Fund deducts a distribution from its net asset value, you will pay the full price for the shares and then receive a portion of the price back in the form of a distribution, which may be subject to federal income tax as described above. In addition, the Fund’s share price may, at any time, reflect undistributed capital gains or income and unrealized appreciation, which may result in future taxable distributions. Such distributions can occur even in a year when the Fund has a negative return. See “Your Account—Dividends and Distributions” for payment schedules, and call the Distributor if you have further questions.

Tax Withholding. The Fund may be required to withhold U.S. federal income tax at a rate of 24% on all distributions and redemption proceeds payable to shareholders who fail to provide their correct taxpayer identification number, fail to make certain required certifications or who have been notified (or when the Fund is notified) by the IRS that they are subject to backup withholding.

Investment in the Subsidiary. The Fund intends to qualify and be treated each year as a “regulated investment company” (“RIC”) under the Code, such that the Fund will not be subject to federal income tax on income and capital gains distributed to shareholders. In order to qualify for the special tax treatment accorded RICs and their shareholders under the Code, a fund must, among other things, derive at least 90% of its gross income from certain specified sources (such income, “qualifying income”). Income from direct investments in commodities and certain commodity-linked derivatives is not qualifying income. Thus, the Fund’s ability to pursue its

investment strategy and achieve its investment objective may be limited by its intention to qualify as a RIC. Any direct investments by the Fund in commodity-linked derivative instruments will be made through the Subsidiary.

Another requirement for qualifying for the special tax treatment accorded RICs and their shareholders under the Code is that a fund must satisfy certain diversification requirements, including the requirement that not more than 25% of the value of the fund’s total assets may be invested in the securities (other than those of the U.S. Government or other RICs) of any one issuer or of two or more issuers which the fund controls and which are engaged in the same, similar, or related trades or businesses. Therefore, so long as the Fund is subject to this limit, it may not invest more than 25% of the value of its total assets in the Subsidiary. If the Fund was to fail to meet the income or diversification test described above, the Fund could, in some cases, cure such failure, including by paying a fund-level tax and, in the case of a diversification test failure, disposing of certain assets. If the Fund was ineligible to, or otherwise did not cure, such failure for any year, its taxable income and gains would be subject to tax at the fund level, and distributions from its earnings and profits would be taxable to shareholders as dividend income.

The foregoing is only intended as a brief summary of certain federal income tax issues relating to investment in the Fund by shareholders subject to federal income tax. Shareholders should consult their tax adviser about the application of the provisions of the tax laws, including state and local tax laws, in light of their particular situation before investing in the Fund.

For a more detailed discussion of federal income taxes, see the Statement of Additional Information.

The Fund provides a variety of services to help you manage your account. If you are investing through a financial intermediary, you may not have access to all of these services. You should consult with your intermediary directly to determine what services are available to you. Class R6 shares may not be available through your financial intermediary.

1. Automatic Dividend Reinvestment Plan. The Fund automatically reinvests all income dividends and capital gain distributions in additional shares at net asset value on the reinvestment date. (For more information, see “Your Account—Dividends and Distributions.”)

3. Automatic Deposit of Dividends. You may elect to have all income dividends and capital gain distributions automatically deposited in a previously established bank account.

Automatic Investment Plan. On your account application for Class N shares or Class I shares of the Fund, you may authorize DST to automatically withdraw an amount of money (minimum $250) from your bank account on the fifth or twentieth day of each month. This amount will be invested in additional shares. You may change your election at any time by providing written notice to DST.

Systematic Withdrawal Plan. You may establish this plan with Class N shares or Class I shares presently held or through a new investment, which should be at least $2,500 for Class N shares and $500,000 for Class I shares. Under this plan, you specify a dollar amount to be paid monthly, quarterly or annually. Shares corresponding to the specified dollar amount are automatically redeemed from your account on the fifth business day preceding the end of the month, quarter or year. While this plan is in effect, all income dividends and capital gain distributions on shares in your account will be reinvested at net asset value in additional shares. There is no charge for withdrawals, but the minimum withdrawal is $250 per month. Depending upon the size of payments requested, and fluctuations in the net asset value of the shares redeemed, redemptions under this plan may reduce or even exhaust your account.

Written Confirmations. Each purchase, exchange or redemption transaction is confirmed in writing to the address of record by giving details of the purchase or redemption.

Suspension of Offering or Rejection of Purchase Orders. The Trust reserves the right to withdraw all or any part of the offering made by this Prospectus, and/or the Trust or the Distributor may reject purchase orders from an investor or an intermediary. From time to time, the Trust may suspend the offering of shares of the Fund to new investors. During the period of such suspension, persons who are already shareholders of the Fund may be permitted to continue to purchase additional shares of the Fund, to have dividends reinvested and to make redemptions. In addition, the Fund may be liquidated and terminated at any time without shareholder approval. Such a liquidation could have negative tax consequences for shareholders and will cause shareholders to incur expenses of liquidation.

Shareholder Rights. All shares of the Fund have equal rights with respect to dividends, assets and liquidation of the Fund and equal, noncumulative voting rights. Noncumulative voting rights allow the holder or holders of a majority of shares, voting together for the election of trustees, to elect all the trustees. All shares of the William Blair Funds will be voted in the aggregate, except when a separate vote by a William Blair Fund is required under the 1940 Act. Shares are fully paid and nonassessable when issued, are transferable without restriction, and have no preemptive or conversion rights. Under Delaware law, the Trust is not required to hold shareholder meetings on an annual basis. As required by law, the Fund will, however, hold shareholder meetings when a sufficient number of shareholders request a meeting, or as deemed desirable by the Board of Trustees, for such purposes as electing or removing trustees, changing fundamental policies or approving a material amendment to the Management Agreement. (For additional information about shareholder voting rights, see the Statement of Additional Information.)

Additional Information on Use of Intermediaries. If you purchase, redeem, or exchange shares through an intermediary, that intermediary may impose charges for its services in addition to the fees charged by the Fund. These charges could reduce your yield or return. In addition, when you place orders with an intermediary, you are not placing your orders directly with the Fund, and you must follow the intermediary’s transaction procedures. Your intermediary may impose different or additional conditions than the Fund on purchases, redemptions and exchanges of Fund shares. These differences may include different minimum initial (and subsequent) investment amounts, exchange policies, fund choices, cut-off times for investment and other trading restrictions. You should consult your intermediary directly for information regarding its conditions and fees. The Fund is not responsible for the failure of your intermediary to carry out its responsibilities.

The Fund’s net asset value is the value of its total assets minus its liabilities. The net asset value per share is determined by dividing the Fund’s net asset value by the number of Fund shares outstanding.

The net asset value per share shall be determined as of the close of regular trading on the New York Stock Exchange (“NYSE”), which is generally 3:00 p.m., Central time (4:00 p.m., Eastern time), on each day when the NYSE is open. The Fund does not price its shares on days when the NYSE is closed for trading.

Quotations of foreign securities in foreign currencies are converted into the United States dollar equivalents at the prevailing market rates as computed by State Street Bank and Trust Company, the Fund’s custodian. Trading in securities on exchanges and over-the-counter markets in Europe and the Far East is normally completed at various times prior to 3:00 p.m., Central time, the current closing time of the NYSE. Trading on foreign exchanges may not take place on every day that the NYSE is open. Conversely, trading in various foreign markets may take place on days when the NYSE is not open and on other days when net asset value is not calculated. Consequently, the value of the net assets held by the Fund may be significantly affected on days when shares are not available for purchase or redemption.

Foreign Equity Securities. The value of foreign equity securities is generally determined based upon the last sale price on the foreign exchange or market on which it is primarily traded and in the currency of that market as of the close of the appropriate exchange or, if there have been no sales during that day, at the mean between the last reported bid and ask prices. The Board of Trustees has determined that the passage of time between when the foreign exchanges or markets close and when the Fund computes its net asset value could cause the value of foreign equity securities to no longer be representative or accurate and, as a result, may necessitate that such securities be fair valued. Accordingly, for foreign equity securities, a Fund may use an independent pricing service to fair value price the security as of the close of regular trading on the NYSE in the event of market movement occurring after the close of regular trading on the foreign exchange or market where the security is primarily traded. As a result, the Fund’s value for a security may be different from the last sale price (or the mean between the last reported bid and ask prices).

Derivative Instruments. Option contracts on securities, currencies and other financial instruments traded on one or more exchanges are valued at their most recent sale price on the exchange on which they are traded most extensively. Option contracts on foreign indices are valued at the settlement price. Futures contracts (and options

and swaps thereon) are valued at the most recent settlement price on the exchange on which they are traded most extensively. Forward foreign currency contracts are valued on the basis of the value of the underlying currencies at the prevailing currency exchange rate as supplied by an independent pricing service.

Subsidiary. The Fund’s shares of the Subsidiary are valued at the net asset value per share of the Subsidiary, which is calculated using the same valuation procedures as the Fund.

The following glossary explains some of the types of securities in which the Fund may invest and investment techniques it may employ, either directly through investment in individual securities or indirectly through various instruments, including ETFs, exchange-traded notes or derivative instruments, and some of the related risks. For more information, please see other sections of this prospectus, including the Summary, Additional Information Regarding Investment Objective and Strategies, and Principal Risks, as well as the Statement of Additional Information.

Asset-Backed Securities. Asset-backed securities are similar in structure to mortgage-backed securities but represent interests in pools of loans, leases or other receivables in place of mortgages. Asset-backed securities are primarily issued by non-government entities.

Corporate Debt Securities. Corporate debt securities are fixed income securities issued by businesses. Notes, bonds, debentures and commercial paper are the most prevalent types of corporate debt securities. The Fund may also purchase interests in bank loans made to companies. The credit risks of corporate debt securities vary widely among issuers.

In addition, the credit risk of an issuer’s debt security may vary based on its priority for repayment. For example, higher ranking (senior) debt securities have a higher priority than lower ranking (subordinated) securities. This means that the issuer might not make payments on subordinated securities while continuing to make payments on senior securities. In addition, in the event of bankruptcy, holders of senior securities may receive amounts otherwise payable to the holders of subordinated securities.

Some subordinated securities, such as trust preferred and capital securities notes, also permit the issuer to defer payments under certain circumstances. For example, insurance companies issue securities known as surplus notes that permit the insurance company to defer any payment that would reduce its capital below regulatory requirements.

Derivatives. The Fund may engage in derivatives for hedging purposes, to maintain liquidity or to seek total return. Derivatives are financial contracts whose value depends on, or is derived from, the value of an underlying asset, reference rate or index. Derivatives are used to earn income and enhance returns, to hedge or adjust the risk profile of its investments, to replace more traditional direct investments, and to obtain exposure to otherwise inaccessible markets. Derivatives include options, futures, forward contracts, swaps and related products.

closed out prior to delivery by entering into an offsetting transaction in a matching futures contract. If the offsetting purchase price is less than the original sale price, the Fund realizes a gain; if it is more, the Fund realizes a loss. Conversely, if the offsetting sale price is more than the original purchase price, the Fund realizes a gain; if it is less, the Fund realizes a loss. The transaction costs must also be included in these calculations. There can be no assurance, however, that the Fund will be able to enter into an offsetting transaction with respect to a particular futures contract at a particular time.

Swaps. A swap is a customized, privately negotiated agreement that obligates two parties to exchange a series of cash flows at specified intervals (payment dates) based upon or calculated by reference to changes in specified process or rates (interest rates in the case of interest rate swaps, currency exchange rates in the case of currency swaps) for a specified amount of an underlying asset (the “notional” principal amount). Cleared swaps are transacted through futures commission merchants that are members of central clearinghouses with the clearinghouse serving as a central counterparty. The swaps market was largely unregulated prior to the enactment of the Dodd-Frank Act. Pursuant to rules promulgated under the Dodd-Frank Act, central clearing of swap agreements is currently required for certain market participants trading certain instruments, and central clearing for additional instruments is expected to be implemented by regulators until the majority of the swaps market is ultimately subject to central clearing.

Credit Default Swaps. A credit default swap is a contract between a buyer and a seller of protection against a pre-defined credit event (e.g., a ratings downgrade or default) on an underlying reference obligation, which may be a single debt instrument or baskets or indices of securities. Credit default swaps are used as a means of “buying” credit protection (i.e., attempting to mitigate the risk of default or credit quality deterioration in some portion of the Fund’s holdings) or “selling” credit protection (i.e., attempting to gain exposure to an underlying issuer’s credit quality characteristics without directly investing in that issuer). The Fund may be a buyer or seller of a credit default swap. Where the Fund is a seller of credit protection, it adds leverage to its portfolio because the Fund is subject to investment exposure on the notional amount of the swap which would be offset to the extent of its uncommitted cash or cash equivalents. The Fund will only sell credit protection with respect to securities in which it would be authorized to invest directly.

If the Fund is a buyer of a credit default swap and no credit event occurs, the Fund will lose its premium payment and recover nothing. However, if the Fund is a buyer and a credit event occurs, the Fund will receive the full notional amount, or “par value,” of the reference obligation in exchange for the reference obligation or a payment equal to the difference in value between the full notional amount, or “par value,” of the reference obligation and the market value of the reference obligation. As a seller, the Fund receives a fixed rate of income reflecting the buyer’s premium payments through the term of the contract (typically between six months and three years), provided that there is no credit event. If a credit event occurs, the Fund must pay the buyer the full notional amount, or “par value,” of the reference obligation in exchange for the reference obligation or the difference in value between the full notional amount, or “par value,” of the reference obligation and the market value of the reference obligation. Credit default swaps may involve greater risks than if the Fund had invested in the reference obligation directly. In addition to the risks applicable to derivatives generally, credit default swaps involve special risks because they may be difficult to value and may be more susceptible to liquidity and credit risk.

Exchange-Traded Funds (“ETFs”). The Fund invests in ETFs. An ETF is an investment company that generally seeks to track the performance of an index by holding in its portfolio shares of all the companies, or a representative sample of the companies, that are components of a particular index. ETFs are traded on a securities exchange based on their market value. When the Fund invests in an ETF, shareholders of the Fund bear their proportionate share of the ETF’s fees and expenses as well as their share of the Fund’s fees and expenses. The Fund may invest in certain ETFs beyond the limits currently imposed by Section 12(d)(1)(A) of the 1940 Act in reliance on orders for exemptive relief obtained by the ETFs from such limitations from the SEC, subject to the ETFs and the Fund complying with the conditions of the orders.

Exchange-Traded Notes (“ETNs”). The Fund may invest in ETNs. An ETN is a security that combines aspects of a bond and an ETF. ETN returns are based upon the performance of a market index or a specific strategy and can be held to maturity as a debt security. ETNs are traded on a securities exchange. Their value is based on their reference index or strategy and the credit quality of the issuer. ETNs are subject to the additional risk that they may trade at a premium or discount to value attributable to their reference index. When the Fund invests in an ETN, shareholders of the Fund bear their proportionate share of the ETN’s fees and expenses, as well as their share of the Fund’s fees and expenses.

Initial Public Offerings (“IPOs”). The Fund may participate in IPOs. IPOs are subject to high volatility and are of limited availability. The Fund’s ability to obtain allocations of IPOs is subject to allocation by members of the underwriting syndicate to various clients and allocation by the Adviser among its clients. When the Fund is small in size, the Fund’s participation in IPOs may have a magnified impact on the Fund’s performance.

Mortgage-Backed Securities. Mortgage-backed securities are securities that directly or indirectly represent a participation in, or are secured by and payable from, mortgage loans secured by real property. There currently are three basic types of mortgage-backed securities: (1) those issued or guaranteed by the U.S. Government or one of its agencies or instrumentalities, such as GNMA (Government National Mortgage Association), FNMA (Federal National Mortgage Association) and FHLMC (Federal Home Loan Mortgage Corporation); (2) those issued by private issuers that represent an interest in or are collateralized by mortgage-backed securities issued or guaranteed by the U.S. Government or one of its agencies or instrumentalities; and (3) those issued by private issuers that represent an interest in or are collateralized by whole mortgage loans or mortgage-backed securities without a government guarantee but that usually have some form of private credit enhancement.

Mortgage-Backed To-Be-Announced (TBA) Securities. The Fund may engage in purchases and sales of mortgage-backed securities eligible to be sold in the to-be-announced (TBA) market, which are transactions in which the Fund purchases or sells mortgage-backed securities on a forward commitment basis for delivery at a future date; however, the specific mortgage-backed securities to be delivered as part of the transaction are not identified until forty-eight hours prior to the settlement date. Mortgage-backed TBA securities can be used for hedging purposes to adjust the risk exposure of a portfolio without having to restructure the portfolio. The Fund may “roll over” mortgage-backed TBA agreements prior to the settlement date in a transaction sometimes referred to as a “TBA roll.” In a TBA roll, the Fund will sell the obligation to purchase the mortgage-backed securities in the TBA agreement prior to the settlement date and will enter into a new mortgage-backed TBA agreement.

Preferred Stock. The Fund may invest in preferred stock. Preferred stock has a preference over common stock in liquidation, but is subordinated to the liabilities of the issuer in all respects. Preferred stock may offer the opportunity for capital appreciation as well as periodic income.

Private Placements. The Fund may purchase securities in private placement transactions. Investments in private placements may be difficult to sell at the time and at the price desired by the Fund; companies making private placements may make less information available than publicly offered companies; and privately placed securities are more difficult to value than publicly traded securities. These factors may have a negative effect on the performance of the Fund. Securities acquired through private placements are not registered for resale in the general securities market and may be classified as illiquid.

Publicly Traded Partnerships (“PTPs”). The Fund may invest in PTPs. PTPs include master limited partnerships and certain other partnerships that meet conditions contained in the Code. A PTP is generally taxed as a corporation for federal income tax purposes. However, if a PTP derives a substantial amount of its income and gains from certain sources, including from the exploration, development, mining or production, processing, refining, transportation or marketing of minerals or natural resources, it may be treated as a partnership for federal income tax purposes. Other PTPs may be treated as partnerships for federal income tax purposes if certain other limited exceptions under the Code apply. PTPs are typically organized as either limited partnerships or limited liability companies and are listed and traded on a U.S. securities exchange.

Real Estate Investment Trusts (“REITs”). The Fund may invest in REITs. REITs are pooled investment vehicles that typically invest directly in real estate, in mortgages and loans collateralized by real estate, or in a combination of the two. “Equity” REITs invest primarily in real estate that produces income from rentals. “Mortgage” REITs invest primarily in mortgages and derive their income from interest payments. REITs usually specialize in a particular type of property and may concentrate their investments in particular geographical areas. REITs issue stocks and most REIT stocks trade on the major stock exchanges or over-the-counter. Exposure to real estate markets, through securities of REITs or other instruments, will be subject to risks of the specific properties or property types and by default rates of borrowers or tenants. Some REITs may have limited diversification and may be subject to risks inherent in investments in a limited number of properties, in a narrow geographic area, or in a single property type. Real estate is also affected by general economic conditions. When growth is slowing, demand for property decreases and prices may decline. Rising interest rates, which drive up mortgage and financing costs, can restrain construction and buying and selling activity, and may reduce the appeal of real estate investments. REITs depend generally on their ability to generate cash flow to make distributions to shareholders or unitholders, and may be subject to defaults by borrowers and self-liquidations. A REIT’s return may be adversely affected when interest rates are high or rising. Distributions to shareholders attributable to dividends received from REITs generally are taxed as ordinary income for federal income tax purposes. In addition, the failure of a REIT to continue to qualify as a REIT for federal income tax purposes would have an adverse effect upon the value of an investment in that REIT.

Repurchase Agreements. Repurchase agreements are instruments under which the Fund acquires ownership of a security, and the seller, a broker-dealer or a bank agrees to repurchase the security at a mutually agreed upon time and price. The repurchase agreement serves to fix the yield of the security during the Fund’s holding period. The Fund currently intends to enter into repurchase agreements only with member banks of the Federal Reserve System or primary dealers in U.S. Government securities and that are cleared through the Fixed Income Clearing Corporation (“FICC”). In all cases, the Adviser must be satisfied with the creditworthiness of the seller before entering into a repurchase agreement. In the event of the bankruptcy or other default of the seller of a repurchase agreement, the Fund could incur expenses and delays enforcing its rights under the agreement, and experience a decline in the value of the underlying securities and loss of income.

Royalty Income Trusts. Royalty income trusts can be organized in a variety of ways in the United States, Canada and other countries. Beneficial units in royalty income trusts generally represent a profits interest in the production of oil or other minerals.

Rule 144A Securities. Rule 144A securities are restricted securities that can be sold to qualified institutional buyers under the Securities Act of 1933, as amended. Investing in Rule 144A securities may increase the illiquidity of the Fund’s investments in the event that an adequate trading market does not exist for these securities.

Short Sales. The Fund can sell securities short. Selling securities short involves selling securities the seller (e.g., the Fund) does not own (but has borrowed) in anticipation of a decline in the market price of such securities. To deliver the securities to the buyer, the seller must arrange through a broker to borrow the securities and, in so doing, the seller becomes obligated to replace the securities borrowed at their market price at the time of the replacement. In a short sale, the proceeds the seller receives from the sale may be retained by the broker until the seller replaces the borrowed securities. The seller may have to pay a premium to borrow the securities and must pay any dividends or interest payable on the securities until they are replaced.

Sovereign Debt. The Fund may invest in sovereign debt issued by a foreign national government. Sovereign debt is typically denominated in a currency other than the issuing government’s domestic currency.

When-Issued and Delayed Delivery Securities. From time to time, in the ordinary course of business, the Fund may purchase newly issued securities appropriate for the Fund on a “when-issued” basis, and may purchase or sell securities appropriate for the Fund on a “delayed delivery” basis. When-issued or delayed delivery transactions involve a commitment by the Fund to purchase or sell particular securities, with payment and delivery to take place at a future date. These transactions allow the Fund to lock in an attractive purchase price or yield on a security the Fund intends to purchase. Normally, settlement occurs within one month of the purchase or sale. During the period between purchase and settlement, no payment is made or received by the Fund and, for delayed delivery purchases, no interest accrues to the Fund. Because the Fund is required to set aside cash or liquid securities at least equal in value to its commitments to purchase when-issued or delayed delivery securities, the Adviser’s ability to manage the Fund’s assets may be affected by such commitments. The Fund will only make commitments to purchase securities on a when-issued or delayed delivery basis with the intention of actually acquiring the securities, but it reserves the right to sell them before the settlement date if it is deemed advisable.

The tables below are intended to help you understand the Fund’s financial performance for the fiscal periods presented. Certain information reflects financial results for a single Fund share. The total return figures show what an investor in the Fund would have earned (or lost) on an investment in the Fund (assuming reinvestment of all dividends and distributions). This information has been derived from the financial statements audited by Ernst & Young LLP, whose report, along with the Fund’s financial statements, is included in the annual report dated December 31, 2019, which is available upon request (see back cover). Net investment income (loss) per share is based on the average shares outstanding during the year.

More information about the Fund is available without charge, upon request, including the following:

The SAI contains more detailed information about the Fund. The current SAI has been filed with the Securities and Exchange Commission and is incorporated by reference into this Prospectus, which means that it is part of this Prospectus for legal purposes.

Text-only versions of Fund documents can be viewed online or downloaded from the EDGAR Database on the SEC’s Internet site at www.sec.gov.

Reports and other information about the Funds are also available on the William Blair Funds website at: https://www.williamblairfunds.com/investor_services/prospectus_reports_forms.fs.

The Trust’s information, including but not limited to the Prospectus, SAI, Semi-Annual and Annual Reports and account application, can be viewed online at www.williamblairfunds.com.

This Statement of Additional Information is not a prospectus. It should be read in conjunction with the corresponding Prospectuses of the above listed Funds dated May 1, 2020. The audited financial statements for the Funds for the year ended December 31, 2019 and the Report of Independent Registered Public Accounting Firm thereon are incorporated by reference from the Annual Report to Shareholders for the year ended December 31, 2019. The Prospectuses and Annual Report to Shareholders may be obtained without charge by calling William Blair Funds (the “Trust”) at the number listed above and on the Funds’ website (https://www.williamblairfunds.com/investor_services/prospectus_reports_forms.fs).

Investment Adviser. As stated in the Prospectus, William Blair Investment Management, LLC (“Adviser” or “WBIM”) is the investment adviser and manager for each Fund. Pursuant to a management agreement (the “Management Agreement”), the Adviser acts as each Fund’s adviser, manages its investments, administers its business affairs, furnishes office facilities and equipment, provides clerical, bookkeeping and administrative services, provides shareholder and information services and permits any of its partners or employees to serve without compensation as trustees or officers of the Fund if elected to such positions. In addition to the management fee, each Fund pays the expenses of its operations, including a portion of the Trust’s general administrative expenses, allocated on the basis of the Fund’s net assets. Expenses that will be borne directly by each Fund include, but are not limited to, the following: the fees and expenses of independent auditors, counsel, custodian and transfer agent, costs of reports and notices to shareholders, printing, postage, costs of calculating net asset value, brokerage commissions or transaction costs, taxes, registration fees, the fees and expenses of qualifying each Fund and its shares for distribution under federal and state securities laws and membership dues in the Investment Company Institute or any similar organization.

In rendering investment advisory services, the Adviser may use the portfolio management, research and other resources of William Blair International, Ltd. (U.K.) (“William Blair U.K.”), an affiliate of the Adviser. William Blair U.K. is not registered with the Securities and Exchange Commission (“SEC”) as an investment adviser under the Investment Advisers Act of 1940, as amended. William Blair U.K. has entered into a Memorandum of Understanding (“MOU”) with the Adviser pursuant to which William Blair U.K. is considered a “participating affiliate” of the Adviser as that term is used in relief granted by the staff of the SEC allowing U.S. registered investment advisers to use portfolio management or research resources of advisory affiliates subject to the supervision of a registered adviser. Investment professionals from William Blair U.K. may render portfolio management, research and other services to the Funds under the MOU and are subject to supervision by the Adviser.

The Management Agreement continues in effect from year to year for each Fund for so long as its continuation is approved at least annually (a) by a majority of the trustees who are not parties to such Management Agreement or interested persons of any such party except in their capacity as trustees of the Trust and (b) by the shareholders of the Fund or the Board of Trustees. The Management Agreement may be terminated at any time upon 60 days’ notice by either party. A Fund may terminate the Management Agreement either by vote of the Board of Trustees or by majority vote of the outstanding shares of the Fund. The Management Agreement may also be terminated at any time either by vote of the Board of Trustees or by majority vote of the outstanding voting shares of a Fund if the Adviser were determined to have breached the Management Agreement. The Management Agreement will terminate automatically upon assignment. The Management Agreement provides that the Adviser shall not be liable for any error of judgment or of law, or for any loss suffered by a Fund in connection with the matters to which the Management Agreement relates, except a loss resulting from willful misfeasance, bad faith or gross negligence on the part of the Adviser in the performance of its obligations and duties, or by reason of its reckless disregard of its obligations and duties under the Management Agreement.

Upon termination of the Management Agreement and when so requested by the Adviser, the Trust or a Fund will refrain from using the name “William Blair” in its name or in its business in any form or combination.

William Blair & Company, L.L.C. is the principal underwriter and distributor of the Trust and is referred to herein as the “Distributor” or “WBC.” WBIM and WBC are referred to herein collectively as “William Blair.”

WBIM and WBC are limited liability companies that are 100% owned by WBC Holdings, L.P., a limited partnership. The affairs of WBIM and WBC are controlled by the general partner of WBC Holdings, L.P., WBC GP L.L.C., which in turn, is controlled by the Executive Committee. The Executive Committee is comprised of Stephanie G. Braming, Ryan J. DeVore, John R. Ettelson, Brent W. Gledhill, John C. Moore, Arthur J. Simon and Jon W. Zindel.

Management Fees. For the services and facilities furnished by the Adviser under the Management Agreement, each Fund pays the Adviser a management fee, which is accrued daily and paid monthly on the first business day of the following month. The annual rate for each Fund expressed as a percentage of average daily net assets is as follows:

Expense Waivers. The Adviser has entered into a contractual agreement with each Fund listed below to waive fees and/or reimburse expenses, if necessary, in order to limit the Fund’s operating expenses, as a percentage of the Fund’s average daily net assets, to the levels reflected in the table below until April 30, 2021 (excluding interest expenses, taxes, brokerage commissions, acquired fund fees and expenses, dividend and interest expenses on short sales, other investment-related costs and extraordinary expenses, such as litigation and other expenses not incurred in the ordinary course of the Fund’s business). The agreement terminates upon the earlier of April 30, 2021 or the termination of the Management Agreement. With respect to the Small-Mid Cap Core Fund, the Adviser is entitled to recoupment of previously waived fees and reimbursed expenses for a period of three

years subsequent to the Fund’s commencement of operations to the extent that such recoupment does not cause the annual Fund operating expenses (after the recoupment is taken into account) to exceed both (1) the expense limit in place when such amounts were waived or reimbursed and (2) the Fund’s current expense limitation.

For the fiscal years ended December 31, 2019, 2018 and 2017, the gross management fees incurred by each Fund, related management fee waivers, net management fees after management fee waivers and other expenses reimbursed by the Adviser were as follows:

Michael P. Balkin is responsible for the management of the Small Cap Growth Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Thomas Clarke is responsible for the management of the Macro Allocation Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Daniel Crowe is responsible for the management of the Mid Cap Growth Fund, the Small-Mid Cap Core Fund, the Small-Mid Cap Growth Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Simon Fennell is responsible for the management of the International Leaders Fund, the International Growth Fund, the Institutional International Growth Fund, the International Small Cap Growth Fund, and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Andrew G. Flynn is responsible for the management of the Global Leaders Fund, the International Small Cap Growth Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

David C. Fording is responsible for the management of the Growth Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

James S. Golan is responsible for the management of the Large Cap Growth Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

James E. Jones is responsible for the management of the Mid Cap Growth Fund, Small-Mid Cap Growth Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Chad M. Kilmer is responsible for the management of the Small-Mid Cap Value Fund, the Small Cap Value Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Robert C. Lanphier IV is responsible for the management of the Mid Cap Growth Fund, the Small-Mid Cap Core Fund, the Small-Mid Cap Growth Fund and other accounts. Effective September 30, 2020, Mr. Lanphier will retire as a portfolio manager. As of December 31, 2019, information on these other accounts is as follows:

Mark T. Leslie is responsible for the management of the Small-Mid Cap Value Fund, the Small Cap Value Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Kathleen M. Lynch is responsible for the management of the Low Duration Fund and other accounts. As of March 31, 2020, information on these other accounts is as follows:

Kenneth J. McAtamney is responsible for the management of the Global Leaders Fund, the International Leaders Fund, the International Growth Fund, the Institutional International Growth Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Todd M. McClone is responsible for the management of the Emerging Markets Leaders Fund, the Emerging Markets Growth Fund, the Emerging Markets Small Cap Growth Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

David S. Mitchell is responsible for the management of the Small-Mid Cap Value Fund, the Small Cap Value Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

John C. Murphy is responsible for the management of the Emerging Markets Leaders Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Casey Preyss is responsible for the management of the Emerging Markets Growth Fund, the Emerging Markets Small Cap Growth Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

David P. Ricci is responsible for the management of the Large Cap Growth Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Ward D. Sexton is responsible for the management of the Small-Mid Cap Core Fund, the Small Cap Growth Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Brian D. Singer is responsible for the management of the Macro Allocation Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Paul J. Sularz is responsible for the management of the Bond Fund, the Low Duration Fund and other accounts. As of December 31, 2019, information on these other accounts is as follows:

Ruta Ziverte is responsible for the management of the Bond Fund, the Income Fund and other accounts. As of March 31, 2020, information on these other accounts is as follows:

Since the portfolio managers manage other accounts in addition to the Funds, conflicts of interest may arise in connection with the portfolio managers’ management of the Funds’ investments on the one hand and the investments of such other accounts on the other hand. However, the Adviser has adopted policies and procedures designed to address such conflicts, including, among others, policies and procedures relating to allocation of investment opportunities, soft dollars and aggregation of trades. For more information on the policies and procedures relating to allocation of investment opportunities, soft dollars and aggregation of trades, see the section entitled “Brokerage and Fund Transactions” in this Statement of Additional Information.

The compensation of the Adviser’s portfolio managers is based on the firm’s mission: “Empower Colleagues, Deliver Client Success and Engage in our Communities.” Messrs. Balkin, Clarke, Crowe, Fennell, Flynn, Fording, Golan, Jones, Kilmer, Lanphier, Leslie, McAtamney, McClone, Mitchell, Murphy, Preyss, Ricci, Sexton and Singer are Partners of the Adviser, and Mses. Lynch and Ziverte and Mr. Sularz are Associates of the Adviser. As of December 31, 2019, compensation for Partners of the Adviser consists of a fixed base salary, a share of the firm’s profits and, in most instances, a discretionary bonus, and compensation for Associates of the Adviser consists of a fixed base salary and a discretionary bonus. The discretionary bonus as well as any potential changes to the Partners’ ownership stakes are determined by the head of William Blair’s Investment Management Department and William Blair’s Executive Committee, and are based on both quantitative and qualitative factors, rather than a formula. The discretionary bonus rewards the specific accomplishments in the prior year, including short-term and long-term investment performance, quality of research ideas, and other contributions to the Adviser and its clients. Changes in ownership stake are based on an individual’s sustained, multi-year contribution to long-term investment performance, and to William Blair’s revenue, profitability, intellectual capital and brand reputation. The compensation process is a subjective one (albeit with many checks and balances and quantitative inputs) that takes into account the factors described above. Portfolio managers do not receive any direct compensation based upon the performance of any individual client account. In addition, there is no formula for evaluating the factors.

The following table sets forth, for each portfolio manager, the dollar range of shares owned in each Fund that the portfolio manager manages as of December 31, 2019.

Distributor. Pursuant to separate Underwriting and Distribution Agreements, William Blair & Company, L.L.C., 150 North Riverside Plaza, Chicago, Illinois 60606, also is the principal underwriter and distributor (“Distributor” or “WBC”) for the continuous offering of shares of the Trust and acts as agent of the Trust in the sale of its shares. The Underwriting Agreement provides that the Distributor will use its best efforts to distribute the Trust’s shares. The Distributor is not compensated under the Underwriting Agreement.

The Distribution Agreement continues in effect from year to year so long as such continuance is approved at least annually by a vote of the Board of Trustees of the Trust, including the Trustees who are not interested persons of the Trust and who have no direct or indirect financial interest in the Distribution Agreement. The Distribution Agreement may be terminated for a Fund at any time without penalty by the Fund or the Distributor. The Distribution Agreement may be terminated for a Fund by vote of a majority of the Board of Trustees, or a majority of the Trustees who are not interested persons of the Trust and who have no direct or indirect financial interest in the Distribution Agreement, or a “majority of the outstanding voting securities” of a Fund, as defined under the Investment Company Act of 1940 (“1940 Act”). The Distribution Agreement may not be amended to increase the fee to be paid by a Fund without approval by a majority of the outstanding voting securities of the Fund and all material amendments must in any event be approved by the Board of Trustees in the manner described above with respect to the continuation of the Distribution Agreement.

Each Fund (with the exception of the Small-Mid Cap Core Fund and the Institutional International Growth Fund, which do not offer Class N shares) has also adopted a plan under Rule 12b-1 (“Distribution Plan”) that provides for fees for shareholder/distribution services for Class N shares. Because Rule 12b-1 fees are paid out of the assets of a Fund’s Class N shares on an ongoing basis, they will increase the cost of an investment in Class N shares and can cost more than other types of sales charges. For its services under the Distribution Plan, the Distributor receives a shareholder/distribution services fee from each Fund, payable monthly, at the annual rate of 0.25% of average daily net assets attributable to Class N shares, respectively, of each Fund except for Class N shares of the Bond Fund, the Income Fund and the Low Duration Fund. For the Class N shares of the Bond Fund, the Income Fund and the Low Duration Fund, the Distributor receives a shareholder/distribution services fee under the Distribution Plan, payable monthly, at the annual rate of 0.15%. For the fiscal year ended December 31, 2019, the Distributor received the following in shareholder/distribution services fees from Class N shares of the Funds:

The Distribution Plan is a compensation plan, which means that the Distributor is compensated regardless of its expenses, as opposed to a reimbursement plan that reimburses only for expenses incurred. For the fiscal year ended December 31, 2019, the Distributor made the following payments to financial services firms who assist in distributing or promoting Class N shares of the Funds:

For the fiscal year ended December 31, 2019, brokers at the Distributor received $102,955 of the Funds’ Rule 12b-1 fees. The Distributor also paid other Fund distribution-related expenses, including advertising, printing and mailing prospectuses to potential investors and overhead expenses.

The Distribution Plan continues in effect from year to year so long as such continuance is approved at least annually by a vote of the Board of Trustees of the Trust, including the Trustees who are not interested persons of the Trust and who have no direct or indirect financial interest in the Distribution Plan or a vote of at least a majority of the outstanding voting securities of Class N of each Fund. The Distribution Plan may be terminated for a Fund at any time without penalty by vote of a majority of the Trustees who are not interested persons of the Trust and who have no direct or indirect financial interest in the Distribution Plan or by vote of a majority of the outstanding securities of Class N shares of a Fund. If the Distribution Plan is terminated in accordance with its terms for a Fund, the obligation of a Fund to make payments to the Distributor pursuant to the Distribution Plan will cease and the Fund will not be required to make any payments past the termination date. Thus, there is no legal obligation for a Fund to pay any expenses incurred by the Distributor in excess of its fees under the Distribution Plan, if for any reason the Plan is terminated in accordance with its terms. Future fees under the Distribution Plan may or may not be sufficient to compensate the Distributor for its expenses incurred. The Distribution Plan may not be amended to increase materially the fee to be paid by a Fund with respect to its Class N shares without approval by a majority of the outstanding voting securities of Class N shares of the Fund and all material amendments must in any event be approved by the Board of Trustees in the manner described above with respect to the continuation of the Distribution Plan.

The Distribution Plan may benefit the Funds and their respective shareholders, by stimulating sales of shares of the Funds and assisting in increasing the asset base of the Funds which may result in greater liquidity, more investment flexibility and achievement of greater economies of scale.

The Trustees and officers of the Trust who are also partners or employees of William Blair as indicated under “Trustees and Officers” have a direct or indirect financial interest in the Distribution Plan and related

Distribution Agreement. None of the Trustees who are not interested persons of the Trust have any direct or indirect financial interest in the Distribution Plan and related Distribution Agreement.

Other Payments to Third Parties and Affiliates. The Funds may reimburse William Blair for fees paid to intermediaries such as banks, broker-dealers, financial advisers or other financial institutions for sub-administration, sub-transfer agency and other services provided to shareholders whose shares are held of record in omnibus, other group accounts, retirement plans or accounts traded through registered securities clearing agents. Such payments and reimbursements are made only on behalf of Class N and Class I shares of a Fund and vary, but generally range up to 0.15% of the assets of the class serviced or maintained by the intermediary or $15 per sub-account maintained by the intermediary.

As described in the Prospectus, William Blair, out of its own resources and without additional cost to the Funds or their shareholders, provides additional cash payments to intermediaries for the provision of services. Such payments are in addition to Rule 12b-1 fees and/or record keeping/sub-transfer agency fees paid by the Funds. Such payments may be made on behalf of Class N, Class I or Class R6 shares of a Fund.

The Distributor currently makes payments from its own assets in connection with the servicing, distribution and/or retention of Fund shares that generally range from 0.01% to 0.15% of the assets of the class serviced. These amounts are subject to change at the discretion of the Distributor.

As of April 1, 2020, William Blair anticipates that the following firms may receive additional payments as described above:

William Blair may enter into additional arrangements or change or discontinue existing arrangements with intermediaries at any time without notice.

In addition to the payments described above, William Blair may make payments to be a named sponsor of investment conferences at which the Funds are marketed. Such payments will be from William Blair’s own resources and will not result in any additional costs to the Funds or their shareholders.

William Blair pays WBC’s Private Wealth division (“Private Wealth”) in amounts that range from 0.10% to 0.35% of the assets of Private Wealth’s advisory clients invested in any Fund’s Class I and Class R6 shares. These revenue sharing payments are made in recognition of the fact that, unlike investments in nonproprietary

funds, Private Wealth does not receive any 12b-1 or other sales or asset based compensation for investments made by its clients into the Fund’s Class I and Class R6 shares. William Blair continues to pay the relevant 12b-1 fees to Private Wealth on any assets of Private Wealth’s brokerage clients invested in any Fund’s Class N shares. However, William Blair shall not make any revenue sharing payments to Private Wealth on any investments by Private Wealth clients in Class N shares.

The prospect of receiving, or the receipt of, additional compensation or promotional incentives described above by Private Wealth or intermediaries may provide Private Wealth or such intermediaries and/or their salespersons with an incentive to favor sales of shares of the Funds over sales of shares of other mutual funds (or non-mutual fund investments) with respect to which Private Wealth or the intermediary does not receive additional compensation or promotional incentives, or receives lower levels of additional compensation or promotional incentives. These payment arrangements, however, will not change the price that an investor pays for Fund shares or the amount that the Funds receive to invest on behalf of an investor. You may wish to take such payment arrangements into account when considering and evaluating any recommendations relating to Fund shares and discuss this matter with your investment dealer/intermediary.

Although the Funds may use an intermediary that sells shares of the Funds to its customers to effect portfolio transactions for the Funds, the Adviser does not consider sales of Fund shares as a factor in the selection of broker-dealers to execute those transactions.

Code of Ethics. The Trust, the Adviser and the Distributor have adopted a joint Code of Ethics (the “Code of Ethics”) in accordance with Rule 17j-1 under the 1940 Act. The Code of Ethics allows access persons to purchase and sell securities for their own accounts, subject to reporting requirements and trading restrictions. The Code of Ethics requires that such persons, among other things, pre-clear their securities transactions, with certain limited exceptions. The Code of Ethics also bans investment personnel from acquiring any securities in an initial public offering. The Code of Ethics prohibits all persons subject to the Code of Ethics from purchasing or selling any security if such person knows or reasonably should know at the time of the transaction that the security was being purchased or sold or was being considered for such purchase or sale by a Fund. Finally, the Code of Ethics prohibits members of a portfolio management team from trading a security within seven calendar days prior to a Fund or an account managed by that portfolio management team trading in that same security. The foregoing description is qualified in its entirety by the Code of Ethics, a copy of which has been filed with the SEC.

Proxy Voting Policy. The Board of Trustees of the Trust has delegated proxy voting authority to the Adviser, who has agreed to vote the Funds’ proxies according to the Adviser’s proxy voting policies and procedures. The Adviser’s Proxy Voting Policy Statement and Procedures (the “Proxy Voting Policy”) provide that the Adviser will vote proxies solely in the best interest of its clients, including the Trust, in their capacity as shareholders of a company. The Proxy Voting Policy addresses, among other things, conflicts of interest that will likely arise between the interests of the Adviser and its affiliates and the interests of the Trust and sets forth the Adviser’s procedures for voting proxies.

The Adviser has engaged Institutional Shareholder Services Inc. (the “Proxy Administrator”) to assist in the administration and voting of proxies. The Adviser’s U.S. Proxy Voting Guidelines and International Proxy Voting Guidelines (the “Guidelines”) set forth the Adviser’s general position on frequent proxy proposals, such as routine matters, shareholder rights, anti-takeover matters, proxy contests, capital structure, executive and director compensation and social and environmental issues. To the extent a particular proposal is not covered by the Guidelines or the Guidelines provide for voting on a “case-by-case” basis, the Proxy Administrator will consult the Adviser’s Proxy Committee, which will review the issues and vote proxies based on information from the company, the Adviser’s internal analysis and third party research services. Although the Guidelines set forth the Adviser’s general position on various proposals, the Adviser may determine under some circumstances to vote contrary to those positions. The Adviser will report any such contrary votes to the Trust’s Board of Trustees.

As indicated above, the Proxy Voting Policy describes the way in which the Adviser will address potential conflicts of interest. If any of the potential conflicts that the Adviser has identified in the Proxy Voting Policy arise with respect to a matter, the Proxy Committee will vote all such proxies in accordance with the Guidelines, unless the Guidelines have no recommendation or provide for a vote on a “case-by-case” basis. In such case, the Proxy Committee will vote consistent with the voting recommendation provided by the Proxy Administrator.

In international markets where share blocking applies, the Adviser typically will not vote proxies due to liquidity constraints. Share blocking is the “freezing” of shares for trading purposes in order to vote proxies. Share blocking typically takes place between one and twenty days before a shareholder meeting, depending on the market. While shares are frozen, they may not be traded. Therefore, there is the potential for a pending trade to fail if trade settlement falls on a date during the blocking period or a Fund would not be able to sell a security if portfolio management believed it advisable if share blocking were in effect.

Information about how the Funds voted proxies during the most recent 12-month period ended June 30 can be obtained by visiting the Trust’s website at www.williamblairfunds.com or by visiting the SEC’s website at www.sec.gov.

Trustees and Officers.^† The trustees and officers of the William Blair Funds, their year of birth, their principal occupations during the last five years, their affiliations, if any, with William Blair and other significant affiliations are set forth below. The address of each officer and trustee is 150 North Riverside Plaza, Chicago, Illinois 60606.

Board of Trustees. The primary responsibility of the Board of Trustees is to represent the interests of the shareholders of the Trust and to provide oversight of the management of the Trust. The Trust’s day to day operations are managed by the Adviser and other service providers who have been approved by the Board. The Board is currently comprised of eight trustees, six of whom are classified under the 1940 Act as “non-interested” persons of the Trust (“Independent Trustees”) and two of whom are classified as an “interested” person of the Trust (“Interested Trustee”). In light of the general characteristics of the Trust, including the number of Funds, the nature of the Funds’ investments and the historical relationship between the Trust and the Adviser, the Board has developed a governance structure that fosters the type of meaningful dialogue between the Adviser and the Independent Trustees that results in an appropriate balance of cooperation with and oversight of the Adviser. The Independent Trustees have appointed Mr. Skelly to serve as Lead Independent Trustee.

The Lead Independent Trustee is responsible for: (i) coordinating activities of the Independent Trustees; (ii) working with the Adviser and counsel to determine the agenda for Board meetings; (iii) serving as the principal contact for and facilitating communication between the Independent Trustees and the Trust’s service providers, particularly the Adviser; and (iv) any other duties that the Independent Trustees may delegate to the Lead Independent Trustee.

Generally, the Board acts by majority vote of all the Trustees, including a majority vote of the Independent Trustees if required by applicable law. The Board has established three standing committees, the Audit Committee, the Nominating and Governance Committee and the Compliance Committee, each comprised entirely of the Independent Trustees, to which it has delegated certain responsibilities as described below. In addition, the Board has also established a Valuation Committee as discussed further below. Each of the three standing Committees reports its activities to the Board on a regular basis. The Board and its committees meet regularly throughout the year to oversee the Trust’s activities, including reviewing at one or more meetings, the Trust’s arrangements with the Adviser and other service providers, the operation of the Trust’s investment policies, compliance and regulatory matters and the Funds’ investment performance. The Independent Trustees are represented by independent legal counsel at Board and committee meetings. As part of its general oversight of the Trust, the Board is involved in the risk oversight of the Trust directly and through its committees. The Board reviews the investment performance of the Funds with the Adviser, including meeting regularly with portfolio managers, at its regularly scheduled quarterly Board meetings. In addition, the Board must approve any material changes to a Fund’s investment policies or restrictions. With respect to compliance matters, the Board is involved in compliance oversight directly and through its Compliance Committee. The Trust’s Chief Compliance Officer provides the annual compliance report required by Rule 38a-1 under the 1940 Act. With respect to valuation, the Board and its Valuation Committee and Audit Committee oversee a pricing committee comprised of Fund officers and Adviser personnel and the Board has approved Valuation Procedures, including fair valuation procedures, applicable to valuing the Fund’s securities, which the Board reviews at least annually. The Audit Committee is responsible for monitoring the Trust’s accounting policies, financial reporting and internal control systems, as well as the work of the independent auditors. On a quarterly basis, the Audit Committee also reviews a report from the Chief Compliance Officer and the pricing committee on valuation and pricing matters.

The Compliance Committee is primarily responsible for overseeing the administration and operation of the compliance policies and procedures of the Trust and its service providers and assisting the Board in fulfilling its responsibility to oversee regulatory and compliance matters involving the Trust. The Compliance Committee receives a quarterly report from the Chief Compliance Officer regarding the operation of the Trust’s compliance policies and procedures, including any material compliance issues that arose during the quarter and meets in executive session with the Chief Compliance Officer at its quarterly meetings. The Nominating and Governance Committee is primarily responsible for the selection of individuals who would qualify to serve as independent trustees and the nomination of trustees for Board membership and for overseeing the administration of the Trust’s Governance Guidelines and Procedures.

The members of the Audit Committee, all of whom are Independent Trustees, include Messrs. Leib (Chairman), Avedisian, Skelly and Zenz and Mses. Barr and McWhorter. The Audit Committee held four meetings in 2019.

The members of the Compliance Committee, all of whom are Independent Trustees, include Mses. Barr (Chairman) and McWhorter and Messrs. Avedisian, Leib, Skelly and Zenz. The Compliance Committee held four meetings in 2019.

The members of the Nominating and Governance Committee, all of whom are Independent Trustees, include Messrs. Avedisian (Chairman), Leib, Skelly and Zenz and Mses. Barr and McWhorter. Pursuant to the Trust’s Governance Guidelines and Procedures, shareholders may submit suggestions for Board candidates by sending a resume of a candidate to the Secretary of the Trust for the attention of the Chairman of the Nominating and Governance Committee. The Nominating and Governance Committee held three meetings in 2019.

The members of the Valuation Committee include Mr. Simon (Interested Trustee) and Mr. Zenz (Independent Trustee). Ms. Braming has been designated as an alternate member in the event that Mr. Simon is unavailable. The other independent trustees are designated as alternate members in the event that Mr. Zenz is unavailable. The Valuation Committee was consulted one time in 2019.

To facilitate shareholder communications with the Board (or with any individual Trustee), shareholders are instructed to forward correspondence (including suggestions for independent trustee candidates) by U.S. mail or other courier service to the Secretary of the Trust, 150 North Riverside Plaza, Chicago, Illinois 60606. Correspondence addressed to the Board will be forwarded to the Chairman of the Nominating and Governance Committee and correspondence addressed to a specific Trustee will be forwarded to that Trustee.

Trustee Qualifications. The following is a brief discussion of the experiences and qualifications that led to the conclusion, as of the date of this SAI, that each current Board member should serve as a Trustee. Generally, the professional, business and educational experience of each Trustee was considered in determining his or her qualifications to serve as a Trustee of the Trust. Each Trustee’s previous record of service, as applicable, as a Trustee or officer of the Trust was considered and served to demonstrate his or her understanding of and commitment to the Trust. With respect to each Trustee, the Board considered, among other factors, the following experiences and qualifications:

The Board considered Vann A. Avedisian’s professional experience serving in various executive positions with companies in the real estate industry, including co-founding and serving as a Managing Director of Oxford Capital Partners, Inc. and, currently, directing the capital market activities of Highgate Holdings, where he is a Principal. The Board considered the executive, financial, operations and risk management experience that Mr. Avedisian gained over the course of his career. The Board also considered Mr. Avedisian’s experience serving as a director of various private and public organizations, including service as the compensation committee chair of a public company.

The Board considered Kathleen T. Barr’s professional experience serving in various executive positions in the financial services industry, including serving as former owner of a registered investment adviser, Chief

Administrative Officer, Senior Vice President and Senior Managing Director of Allegiant Asset Management Company (merged with PNC Capital Advisors, LLC in 2009) and as Chief Administrative Officer, Chief Compliance Officer and Senior Vice President of PNC Funds and PNC Advantage Funds (f/k/a Allegiant Funds). The Board considered the executive, compliance, investment product, distribution, administrative, operations and risk management experience that Ms. Barr gained over the course of her career. The Board also considered Ms. Barr’s experience serving on the board of another mutual fund group and serving as a member of the Governing Council of the Independent Directors Council.

The Board considered Stephanie G. Braming’s professional experience in the financial services industry, including as a Partner of William Blair Investment Management, LLC and William Blair & Company, L.L.C. where she serves on the executive committee and as the global head of William Blair’s Investment Management division. The Board considered the executive, investment and financial experience that Ms. Braming gained over the course of her career. The Board also considered that because of Ms. Braming’s positions with William Blair, she is involved in the day-to-day management of the Adviser and the Trust.

The Board considered Daniel N. Leib’s professional experience serving in various executive positions with companies in the printing, advertising and marketing and retail industries, including currently serving as Chief Executive Officer of Donnelley Financial Solutions, Inc., and prior thereto serving in roles as Executive Vice President, Chief Financial Officer, Senior Vice President and Treasurer, of R.R. Donnelley & Sons Company. The Board considered the executive, financial (including treasury and pension oversight), operations and risk management experience that Mr. Leib gained over the course of his career.

The Board considered the executive, audit, and risk management experience that Dorri C. McWhorter gained over the course of her career. The Board considered Ms. McWhorter’s professional experience as a certified public accountant and auditor, including her experience as a partner at Crowe LLP, where she was responsible for risk consulting, and her experience as Director of Internal Audit for a public company. The Board likewise considered Ms. McWhorter’s executive experience, including her current position as Chief Executive Officer of YWCA Metropolitan Chicago. Further, the Board considered Ms. McWhorter’s service as a board member for various professional organizations.

The Board considered Arthur J. Simon’s professional training and experience as an attorney and his executive experience gained as a Partner of William Blair Investment Management, LLC and William Blair & Company, L.L.C., including serving on William Blair’s executive committee and as General Counsel of William Blair. The Board considered the legal and executive experience that Mr. Simon gained over the course of his career. The Board considered that because of Mr. Simon’s position with William Blair, he is involved in the day-to-day management of the Adviser and the Distributor.

The Board considered Thomas J. Skelly’s professional experience serving in various executive positions at Accenture, including his experience as the managing partner of Accenture’s U.S. operations and as the chairman of the Accenture Pension Fund. The Board considered the executive, operations, information technology, financial and investment experience that Mr. Skelly gained over the course of his career. The Board also considered Mr. Skelly’s experience serving as a director or trustee of a public company and various private organizations. Further, the Board considered Mr. Skelly’s service on various advisory boards for private and public companies.

The Board considered Steven R. Zenz’s professional training and experience as a certified public accountant and auditor, including his experience as a partner of KPMG LLP providing advice to clients in a variety of industries and serving as Partner in Charge of KPMG’s Minneapolis-based Investment Banking Practice as well as various other leadership roles within KPMG LLP. The Board considered the executive, financial and audit experience that Mr. Zenz gained over the course of his career. Further, the Board considered Mr. Zenz’s experience serving on the boards of other public and private companies and organizations.

References to the experience and qualifications of the Trustees are pursuant to requirements of the SEC, do not constitute holding out of the Board or any Trustee as having any special expertise and shall not impose any greater responsibility or liability on any such person or on the Board by reason thereof.

Trustee Compensation. Trustees who are not affiliated with the Adviser receive an annual retainer plus per meeting fees (which vary depending on whether attendance is in person or by telephone). Trustees also receive compensation for attendance at committee meetings (except for the Valuation Committee for which the Trustees receive no additional compensation). The Lead Independent Trustee and the Chairmen of the Audit Committee, Compliance Committee and Nominating and Governance Committee each receive an additional retainer for serving in such positions. The Independent Trustees receive one-half of the annual retainer in cash and the other half is invested in Fund shares as directed by the Independent Trustees. The Trustees and officers affiliated with the Adviser receive no compensation from the Trust.

The following table sets forth the compensation earned by the Independent Trustees from the Funds and the Trust for the fiscal year ended December 31, 2019:

Trustees’ and Officers’ Holdings of Fund Shares. The following table sets forth, for each Trustee, the dollar range of shares owned in each Fund as of December 31, 2019, as well as the aggregate dollar range of shares owned in the Trust as of the same date.

As of December 31, 2019, the Trustees and officers, as a group, owned (or held or shared investment or voting power with respect to) more than 1% of the outstanding shares of each Fund listed in the table below. For all other Funds, the Trustees and officers, as a group, owned less than 1% of the outstanding shares of each class of the Fund. Shareholders who have the power to vote a large percentage of shares (at least 25%) of a Fund can control the Fund and could determine the outcome of a shareholders meeting.

Trustees’ Holdings in Certain Affiliates of the Adviser. In addition to investing in the various Funds, Independent Trustees may from time to time invest in limited partnerships that are managed by the Adviser or an affiliate of the Adviser. The Independent Trustees may also from time to time, invest in third party investment ventures in which affiliates and employees of the Adviser also invest. In addition, Messrs. Avedisian and Skelly employ the Adviser to manage assets that they control.

Principal Shareholders. The following table provides certain information as of April 3, 2020 with respect to persons known to the Trust to be record holders of 5% or more of a class of shares of a Fund. Shareholders who have the power to vote a large percentage of shares (at least 25%) of a Fund can control the Fund and could determine the outcome of a shareholders’ meeting.

Brokerage and Fund Transactions. Decisions on portfolio transactions (including the decision to buy or sell, the appropriate price, allocation of brokerage, use of a broker as agent or dealer as principal and negotiation of commissions) normally are made by the Adviser. In purchasing and selling portfolio securities, the Trust seeks to obtain the most favorable overall result, taking into account the net price, the method of execution and research services provided by the broker. Such research services include economic forecasts and analytical, narrative and statistical reports on industries and companies for consideration by the Trust and the Adviser’s other clients.

Portfolio transactions may increase or decrease the return of a Fund depending upon the Adviser’s ability to efficiently execute such transactions. A portfolio turnover rate for any year is determined by dividing the lesser of sales or purchases (excluding in either case cash equivalents, such as short-term corporate notes) by the portfolio’s monthly average net assets and multiplying by 100 (with all securities with maturities and expirations of one year or less excluded from the computation). A Fund’s turnover rate will vary from year to year due to,

among other things, a fluctuating volume of shareholder purchase and redemption orders, market conditions, and/or changes in the Adviser’s investment outlook. The Small Cap Value Fund’s portfolio turnover rate varied significantly in 2019 compared to 2018 as a result of a significant redemption order at the end of 2019.

Selection of a broker for a particular portfolio transaction depends on many factors, some of which are subjective and that include the net price, confidentiality, reliability, integrity, size and nature of the transaction and the market in which it is to occur and any research or other services that the broker has provided. The Adviser does not consider the sale of Fund shares in selecting brokers. Transactions in over-the-counter securities are generally executed as principal trades with primary market makers, except where it is believed that a better combination of price and execution could otherwise be obtained. The Adviser determines the overall reasonableness of brokerage commissions and of premiums and discounts on principal transactions (which do not involve commissions) by review of comparable trades for the Adviser’s other clients and in the market generally. If more than one broker is believed to be equally qualified to effect a portfolio transaction, the Adviser may assign the transaction to a broker that has furnished research services, but the Adviser has no agreement, formula or policy as to allocation of brokerage.

The Trust may pay to brokers that provide research services to the Adviser a commission higher than another broker might have charged if the Adviser determines that the commission is reasonable in relation to the value of the brokerage and research services that are provided, viewed in terms of either the particular transaction or the Adviser’s overall responsibility to its advisory accounts. The extent to which such commissions exceed commissions solely for execution cannot be determined, but such research services, which are involved in portfolio transactions for the Trust and for the Adviser’s other advisory accounts, can be of benefit to both the Trust and such other accounts. The value of research services that are provided by brokers who handle portfolio transactions for the Trust cannot be precisely determined and such services are supplemental to the Adviser’s own efforts, which are undiminished thereby. The Adviser does not believe that its expenses are reduced by reason of such services, which benefit the Trust and the Adviser’s other clients. The Adviser receives research products and services from broker/dealers and third parties in the form of written reports on individual companies and industries of particular interest to the Adviser, general economic conditions, pertinent federal and state legislative developments and changes in accounting practices; direct access by telephone or meetings with leading research analysts throughout the financial community and industry experts; comparative performance and evaluation and technical measurement services for issuers, industries and the market as a whole; access to and monitoring of equity valuation models; and services from recognized experts on investment matters of particular interest to the Adviser.

The Adviser also participates in “commission sharing arrangements” and “client commission arrangements” under which the Adviser may effect transactions through a broker-dealer and request that the broker-dealer allocate a portion of the commissions or commission credits to another firm that provides research to the Adviser. The Adviser also utilizes Electronic Communication Networks and other alternative trading platforms (collectively, “ECNs”) to execute trades in connection with commission sharing arrangements. In such instances, the Adviser will execute a trade with the ECN and pay a commission to the ECN. The ECN will then credit a negotiated portion of the commission to a broker as requested by the Adviser for the purpose of funding a pool to be used to pay for research services received by the Adviser from other firms. In addition, the ECN will credit a further portion of the commission to the broker for its services in administering the commission sharing arrangements. The commission sharing and client commission arrangements, as well as the research provided in connection with such arrangements, are intended to comply with Section 28(e) of the Securities Exchange Act of 1934, as interpreted by the SEC. The Adviser believes that participating in commission sharing and client commission arrangements enable the Adviser to consolidate payments for research through one or more channels using accumulated client commissions or credits from transactions executed through a particular broker-dealer or ECN to obtain research provided by other firms. Such arrangements also help to provide the continued receipt of research services while facilitating best execution in the trading process. The Adviser also believes such research services are useful in its investment decision-making process by, among other things, providing access to a variety of high quality research, access to individual analysts and availability of resources that might not be available to the Adviser absent such arrangements.

During the fiscal years ended December 31, 2019, 2018 and 2017, each Fund paid total brokerage fees in the amounts shown in the table below. None of the brokerage fees paid by the Funds were paid to a broker that was an affiliated person of the Trust or to a broker of which an affiliated person was an affiliated person of the Trust or of the Adviser.

The Adviser does not use the Funds’ brokerage commissions to pay for non-research items. During the fiscal year ended December 31, 2019, the following amounts of brokerage commissions for each Fund were used to pay third parties for third party research.

Purchases and sales of fixed income securities for the Bond Fund, the Income Fund, the Low Duration Fund and the Macro Allocation Fund usually are principal transactions, either directly with the issuer or with an underwriter or market maker, in which case brokerage commissions are not paid by the Fund. Brokerage commissions, if any, paid by the Bond Fund, the Income Fund and the Low Duration Fund during the fiscal years ended December 31, 2019, 2018 and 2017 are shown in the table above. No brokerage commissions were paid for purchases and sales of fixed income securities by the Macro Allocation Fund during the fiscal years ended December 31, 2019, 2018 and 2017. Purchases from underwriters will include a commission or concession paid

by the issuer to the underwriter and purchases from dealers serving as market makers will include the spread between the bid and asked prices. The primary consideration in the allocation of transactions is prompt execution of orders in an effective manner at the most favorable price.

Generally, the investment decisions for the Funds are reached independently from those for other accounts managed by the Adviser. However, some other accounts may make investments in the same type of instruments or securities as the Funds at the same time as the Funds. Such other accounts may include private investment funds operated by the Adviser that compete directly with the Funds for securities—particularly those sold in private placements or initial public offerings (“IPOs”); the Adviser and its personnel may stand to benefit more personally from good investment performance by these private investment funds than by equivalent performance of the Funds. In those instances where the Funds and another client of the Adviser trade in the same type of instrument at the same time, the Adviser has established allocation procedures to allocate such trades among its various clients and the Funds equitably. In some cases this procedure may affect the size or price of the position obtainable for the Funds.

Although the Adviser may execute portfolio transactions for the Funds under conditions set forth in applicable rules of the SEC and in accordance with procedures adopted by the Board of Trustees, the Adviser or any affiliated broker-dealer of the Adviser is not compensated for executing portfolio transactions for the Funds. The Funds may purchase securities from other members of an underwriting syndicate of which the Adviser or an affiliated broker-dealer is a participant, but only under conditions set forth in applicable rules of the SEC and in accordance with procedures adopted by the Board of Trustees.

The Funds are required to identify any securities of their “regular brokers or dealers” (as defined in the 1940 Act) that the Funds have acquired during the most recent fiscal year. The following table sets forth the securities of its regular broker-dealers, if any, held by each Fund as of December 31, 2019:

Disclosure of Portfolio Holdings. The Funds do not disseminate nonpublic information about portfolio holdings except in accordance with the Trust’s policies and procedures. The Trust’s policies and procedures governing disclosure of portfolio holdings permit nonpublic portfolio holding information to be shared with the Trust’s service providers and others who generally need access to such information in the performance of their duties and responsibilities, such as the Trust’s Adviser, custodian, pricing services, fund accountants, independent public accountants, attorneys, officers and trustees. In addition, a Fund’s portfolio holdings may be discussed with third parties (e.g., broker/dealers) for the purpose of analyzing or trading such securities. Portfolio holding information may also be disclosed to rating agencies and companies that collect information about mutual funds

(such as Morningstar, Inc., Standard & Poor’s, a division of The McGraw-Hill Companies, Inc., and Broadridge Financial Solutions, Inc.) only after its public disclosure.

Each Fund’s (except for the Small Cap Growth Fund and the Small Cap Value Fund) complete portfolio holdings as of the end of each calendar month are posted on the Trust’s website, https://www.williamblairfunds.com/investor_services/fund_literature.fs, on or about fifteen days after the month-end. The Small Cap Growth Fund’s and the Small Cap Value Fund’s complete portfolio holdings as of the end of each calendar month are posted on the Trust’s website on or about thirty days after the month-end. This posted information generally remains accessible for thirty days, until the Trust posts the information for the next calendar month to the Trust’s website. A Fund’s specific portfolio holdings may be disclosed sooner than fifteen or thirty days, as applicable, after the month-end if they are publicly disseminated (e.g., via the Trust’s website or interviews with the news media).

Any disclosure of portfolio holdings or characteristics not addressed by the Trust’s policies and procedures must be submitted to the Chief Compliance Officer for review before dissemination. Prior to such disclosure, the Chief Compliance Officer must make a good faith determination in light of the facts then known that a Fund has a legitimate business purpose for providing the information, that the disclosure is in the best interest of the Fund and that the recipient assents or otherwise has a duty to keep information confidential and agrees in writing not to disclose, trade or make any investment recommendation based on the information received. No compensation or other consideration is received by the Trust or any affiliates of the Trust for disclosure of portfolio holdings information.

The Chief Compliance Officer provides the Board of Trustees or the Compliance Committee thereof with reports of any potential exceptions to, or violations of, the Trust’s policies and procedures governing disclosure of portfolio holdings that are deemed to constitute a material compliance matter. Each Fund discloses its portfolio holdings to the extent required by law.

The Trust has adopted certain fundamental investment restrictions for each Fund that, along with the Fund’s investment objective, cannot be changed without approval by holders of a “majority of the outstanding voting securities” of the Fund, which is defined in the 1940 Act to mean the lesser of (a) 67% of the shares of the portfolio at a meeting where more than 50% of the outstanding voting shares of the Fund are present in person or by proxy; or (b) more than 50% of the outstanding voting shares of the Fund. Each Fund has elected to be classified as a diversified series of an open-end management investment company. As a diversified series of an open-end management investment company, each Fund may not, with respect to 75% of its total assets, purchase the securities of any issuer (except securities issued or guaranteed by the U.S. government, its agencies or instrumentalities) if, as a result, (i) more than 5% of the Fund’s total assets would be invested in the securities of that issuer or (ii) the Fund would hold more than 10% of the outstanding voting securities of that issuer. Each Fund’s election to be classified as diversified under the 1940 Act may not be changed without approval by holders of a majority of the outstanding voting securities of the Fund. All percentage restrictions on investments apply at the time the investment is made and shall not be considered to violate the applicable limitation unless, immediately after or as a result of the investment, a violation of the restriction occurs. There can be no assurance that a Fund will meet its investment objective.

Except as otherwise noted, the following fundamental investment restrictions apply to each Fund:

Concentration. Each Fund except the Small-Mid Cap Value Fund and the International Leaders Fund:

The Fund will not make investments that will result in the concentration (as that term is defined in the 1940 Act, any rule or order thereunder, or SEC staff interpretation thereof) of its investments in the securities of issuers primarily engaged in the same industry, provided that this restriction does not limit the Fund from investing in obligations issued or guaranteed by the U.S. Government, its agencies or instrumentalities, or in tax-exempt securities.

This restriction also does not limit the Fund from investing in instruments, such as repurchase agreements, secured by obligations issued or guaranteed by the U.S. Government, its agencies or instrumentalities.

The SEC staff currently interprets concentration to mean investing more than 25% of a fund’s net assets in a particular industry or group of industries.

Senior Securities and Borrowing. The Fund may not borrow money or issue senior securities, except as the 1940 Act, any rule or order thereunder, or SEC staff interpretation thereof, may permit.

Underwriting. The Fund may not underwrite the securities of other issuers, except that the Fund may engage in transactions involving the acquisition, disposition or resale of its portfolio securities under circumstances where it may be considered to be an underwriter under the Securities Act of 1933.

Real Estate. The Fund may not purchase or sell real estate unless the real estate is acquired as a result of ownership of securities or other instruments; and provided that this restriction does not prevent the Fund from investing in issuers that invest, deal or otherwise engage in transactions in real estate or interests therein, or investing in securities that are secured by real estate or interest therein.

Commodities. Each Fund except the Small-Mid Cap Value Fund, the International Leaders Fund, the Emerging Markets Small Cap Growth Fund and the Macro Allocation Fund:

The Fund may not purchase or sell physical commodities unless acquired as a result of ownership of securities or other instruments; however, this restriction shall not prevent the Fund from engaging in transactions involving futures contracts, options or other derivative instruments or investing in securities that are secured by physical commodities.

Small-Mid Cap Value Fund, International Leaders Fund and Emerging Markets Small Cap Growth Fund:

The Fund may not purchase or sell commodities unless acquired as a result of ownership of securities or other instruments; however, this restriction shall not prevent the Fund from engaging in transactions involving futures contracts, options or other derivative instruments, investing in securities that are secured by commodities or investing in companies or other entities that are engaged in a commodities or commodities trading business or that have a significant portion of their assets in commodities related investments.

Lending. The Fund may not make loans, provided that this restriction does not prevent the Fund from purchasing debt obligations, entering into repurchase agreements, loaning its assets to broker/dealers or institutional investors, and investing in loans, including assignments and participation interests.

The following are each Fund’s non-fundamental operating policies, which may be changed by the Trust’s Board of Trustees without shareholder approval.

The Growth Fund, Large Cap Growth Fund, Mid Cap Growth Fund, Small-Mid Cap Core Fund, Small-Mid Cap Growth Fund, Small-Mid Cap Value Fund, Small Cap Growth Fund, Small Cap Value Fund, Global Leaders Fund, International Leaders Fund, International Growth Fund, Institutional International Growth Fund, International Small Cap Growth Fund, Emerging Markets Leaders Fund, Emerging Markets Growth Fund and Emerging Markets Small Cap Growth Fund may not:

Under normal market conditions, the Large Cap Growth Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of large cap companies.

Under normal market conditions, the Mid Cap Growth Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of mid cap companies.

Under normal circumstances, the Small-Mid Cap Core Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small capitalized (“small cap”) and medium capitalized (“mid cap”) companies.

Under normal market conditions, the Small-Mid Cap Growth Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small and mid cap companies.

Under normal market conditions, the Small-Mid Cap Value Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small and mid cap companies.

Under normal market conditions, the Small Cap Growth Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small cap companies.

Under normal market conditions, the Small Cap Value Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small cap companies.

Under normal market conditions, the Global Leaders Fund invests at least 80% of its total assets in a diversified portfolio of equity securities, including common stock and other forms of equity investment (e.g., securities convertible into common stocks), issued by companies of all sizes worldwide that the Adviser believes have above-average growth, profitability and quality characteristics.

Under normal market conditions, the International Growth Fund and Institutional International Growth Fund each invest at least 80% of its total assets in a diversified portfolio of equity securities, including common stock and other forms of equity investment (e.g., securities convertible into common stocks), issued by companies of all sizes domiciled outside the U.S. that the Adviser believes have above-average growth, profitability and quality characteristics.

Under normal market conditions, the International Small Cap Growth Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in stocks of small cap companies.

Under normal market conditions, the Emerging Markets Leaders Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in emerging markets securities.

Under normal market conditions, the Emerging Markets Growth Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in emerging markets securities.

Under normal market conditions, the Emerging Markets Small Cap Growth Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of emerging market small cap companies.

Under normal market conditions, the Bond Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in bonds.

Each Fund will provide shareholders with at least 60 days’ prior notice of any change in its 80% investment policy.

With respect to the Growth Fund, the Large Cap Growth Fund, the Mid Cap Growth Fund, the Small-Mid Cap Core Fund, the Small-Mid Cap Growth Fund, the Small-Mid Cap Value Fund, the Small Cap Growth Fund and the Small Cap Value Fund: each Fund may invest up to 15% of its net assets (20% for the Small-Mid Cap Value Fund and the Small Cap Growth Fund) in foreign securities, which may include American Depository Receipts or substantially similar investments that are based on foreign securities; however, each Fund may invest only up to 5% of its net assets directly in foreign securities, except the Small-Mid Cap Core Fund.

With respect to the Global Leaders Fund, the International Leaders Fund, the International Growth Fund, the Institutional International Growth Fund, the International Small Cap Growth Fund, the Emerging Markets Leaders Fund, the Emerging Markets Growth Fund and the Emerging Markets Small Cap Growth Fund: for liquidity purposes, up to 20% of the Fund’s assets may be held in cash (U.S. dollars and foreign currencies) or in short-term securities and domestic and foreign money market instruments, such as government obligations, certificates of deposit, bankers’ acceptances, time deposits, commercial paper and short-term corporate debt securities. None of the Funds have specific rating requirements for their short-term securities; however, other than with respect to the Macro Allocation Fund, the Adviser presently does not intend to invest more than 5% of any Fund’s net assets in securities rated lower than investment grade.

The Prospectus describes each Fund’s investment objective as well as certain investment policies and investment techniques that the Fund may employ in pursuing its investment objective. The following discussion supplements the discussion contained in the Prospectus, including the Investment Glossary at the end of the Prospectus. Not all of the Funds may invest in all of the types of investments listed below.

Borrowings. Note: Presently, the Funds only intend to borrow from banks for temporary or emergency purposes. However, each Fund may borrow money from banks and make other investments or engage in other transactions permissible under the 1940 Act that may be considered a borrowing (such as mortgage dollar rolls and reverse repurchase agreements).

Business Development Companies (“BDCs”). Consistent with its investment objective and policies and subject to the limitations of the 1940 Act, each Fund except the Macro Allocation Fund may invest in BDCs. BDCs are a type of closed-end fund regulated under the 1940 Act, which typically invest in and lend to small- and medium-sized private companies that may lack access to public equity markets for capital raising. Under the 1940 Act, BDCs must invest at least 70% of the value of their total assets in certain asset types, which are typically the securities of private U.S. businesses. Additionally, BDCs must make available significant managerial assistance to the issuers of such securities. BDCs are not taxed on income distributed to shareholders provided they qualify as a regulated investment company under the Internal Revenue Code of 1986, as amended (the “Code”). The Funds will indirectly bear their proportionate share of any management and other expenses charged by the BDCs in which they invest.

Because BDCs typically invest in small and medium-sized companies, a BDC’s portfolio is subject to the risks inherent in investing in smaller companies, including that portfolio companies may be dependent on a small number of products or services and may be more adversely affected by poor economic or market conditions. Some BDCs invest substantially, or even exclusively, in one sector or industry group and therefore the BDC may be susceptible to adverse conditions and economic or regulatory occurrences affecting the sector or industry group, which tends to increase volatility and result in higher risk. Investments in BDCs are also subject to management risk, including management’s ability to meet the BDC’s investment objective, and management’s ability to manage the BDC’s portfolio during periods of market turmoil and as investors’ perceptions regarding a BDC or its underlying investments change.

Collateralized Obligations. General Information on Mortgage-Backed Securities. Collateralized obligations include mortgage-backed collateralized obligations (“mortgage-backed securities”). Mortgage-backed securities are securities that directly or indirectly represent a participation in, or are secured by and payable from, mortgage loans secured by real property. There currently are three basic types of mortgage-backed securities: (1) those issued or guaranteed by the U.S. Government or one of its agencies or instrumentalities, such as GNMA (Government National Mortgage Association), FNMA (Federal National Mortgage Association) and FHLMC (Federal Home Loan Mortgage Corporation); (2) those issued by private issuers that represent an interest in or are collateralized by mortgage-backed securities issued or guaranteed by the U.S. Government or one of its agencies or instrumentalities; and (3) those issued by private issuers that represent an interest in or are collateralized by whole mortgage loans or mortgage-backed securities without a government guarantee but that usually have some form of private credit enhancement.

The yield characteristics of mortgage-backed securities differ from traditional debt securities. Among the major differences are that interest and principal payments are made more frequently, usually monthly, and that principal may be prepaid at any time because the underlying mortgage loans generally may be prepaid at any time. The rate of pre-payments on underlying mortgages will affect the price and volatility of a mortgage-backed security, and may have the effect of shortening or extending the effective duration of the mortgage-backed security relative to what was anticipated at the time of purchase. To the extent that unanticipated rates of pre-payment on underlying mortgages increase the effective duration of a mortgage-backed security, the volatility of such mortgage-backed security can be expected to increase. For example, if a Fund purchases such a security at a premium, a prepayment rate that is faster than expected will reduce yield to maturity, while a prepayment rate that is slower than expected will increase yield to maturity. Conversely, if a Fund purchases these securities at a discount, faster than expected prepayments will increase yield to maturity, while slower than expected prepayments will reduce it.

Prepayments on a pool of mortgage loans are influenced by a variety of economic, geographic, social and other factors, including changes in mortgagors’ housing needs, job transfers, unemployment, mortgagors’ net equity in the mortgaged properties and servicing decisions. Generally, however, prepayments on fixed-rate mortgage loans will increase during a period of falling interest rates and decrease during a period of rising interest rates. Accordingly, amounts available for reinvestment by a Fund are likely to be greater during a period of declining interest rates and, as a result, are likely to be reinvested at lower interest rates than during a period of rising interest rates. Mortgage-backed securities may decrease in value as a result of increases in interest rates and may benefit less than other fixed income securities from declining interest rates because of the risk of prepayment.

Guaranteed Mortgage Pass-Through Securities. Mortgage pass-through securities represent participation interests in pools of residential mortgage loans originated by United States governmental or private lenders and guaranteed, to the extent provided in such securities, by the U.S. Government or one of its agencies or instrumentalities. Such securities, which are ownership interests in the underlying mortgage loans, differ from conventional debt securities, which provide for periodic payment of interest in fixed amounts (usually semi-annually) and principal payments at maturity or on specified call dates. Mortgage pass-through securities provide for monthly payments that are a “pass-through” of the monthly interest and principal payments (including any prepayments) made by the individual borrowers on the pooled mortgage loans, net of any fees paid to the guarantor of such securities and the servicers of the underlying mortgage loans. The guaranteed mortgage pass-through securities in which a Fund will invest will include those issued or guaranteed by GNMA, FNMA and FHLMC.

GNMA is a wholly owned corporate instrumentality of the United States within the Department of Housing and Urban Development. The National Housing Act of 1934, as amended (the “Housing Act”), authorizes GNMA to guarantee the timely payment of the principal of and interest on certificates (“Ginnie Mae Certificates”) that are based upon and backed by a pool of mortgage loans insured by the Federal Housing Administration under the Housing Act or Title V of the Housing Act of 1949 (FHA Loans), or guaranteed by the Veterans’ Administration under the Servicemen’s Readjustment Act of 1944, as amended (VA Loans), or by pools of other eligible mortgage loans. Ginnie Mae Certificates represent a pro rata interest in one or more pools of eligible mortgage loans. The Housing Act provides that the full faith and credit of the U.S. Government is pledged to the payment of all amounts that may be required to be paid under any guarantee. In order to meet its obligations under such guarantee, GNMA is authorized to borrow from the United States Treasury with no limitations as to amount.

FNMA is a federally chartered corporation organized and existing under the Federal National Mortgage Association Charter Act. FNMA provides funds to the mortgage market primarily by purchasing home mortgage loans from local lenders, thereby replenishing their funds for additional lending. FNMA acquires funds to purchase home mortgage loans from many capital market investors that may not ordinarily invest in mortgage loans directly, thereby expanding the total amount of funds available for housing.

Each Fannie Mae Certificate will entitle the registered holder thereof to receive amounts representing the holder’s pro rata interest in scheduled principal payments and interest payments (at such Fannie Mae

Certificate’s pass-through rate, which is net of any servicing and guarantee fees on the underlying mortgage loans) and any principal prepayments on the mortgage loans in the pool represented by such Fannie Mae Certificate and such holder’s proportionate interest in the full principal amount of any foreclosed or otherwise finally liquidated mortgage loan. The full and timely payment of principal of and interest on each Fannie Mae Certificate will be guaranteed by FNMA, which guarantee is not backed by the full faith and credit of the U.S. Government. FNMA has limited rights to borrow from the United States Treasury.

FHLMC is a corporate instrumentality of the United States created pursuant to the Emergency Home Finance Act of 1970, as amended. FHLMC was established primarily for the purpose of increasing the availability of mortgage credit for the financing of needed housing. The principal activity of FHLMC currently consists of the purchase of first lien, conventional, residential mortgage loans and participation interests in such mortgage loans and the resale of the mortgage loans so purchased in the form of mortgage securities, primarily Freddie Mac Certificates.

FHLMC guarantees to each registered holder of a Freddie Mac Certificate the timely payment of interest at the rate provided for by such Freddie Mac Certificate, whether or not received. FHLMC also guarantees to each holder of a Freddie Mac Certificate ultimate collection of all principal of the related mortgage loans, without any offset or deduction, but does not always guarantee the timely payment of scheduled principal. FHLMC may remit the amount due on account of its guarantee of collection of principal at any time after default on an underlying mortgage loan, but not later than 30 days following (i) foreclosure sale, (ii) payment of a claim by any mortgage insurer or (iii) the expiration of any right of redemption, whichever occurs last, but in any event no later than one year after demand has been made upon the mortgagor for accelerated payment of principal. The obligations of FHLMC under its guarantee are obligations solely of FHLMC and are not backed by the full faith and credit of the U.S. Government. FHLMC has limited rights to borrow from the United States Treasury.

Until 2008, FNMA and FHLMC were government-sponsored corporations owned entirely by private stockholders. On September 7, 2008, the U.S. Treasury announced a federal takeover of FNMA and FHLMC, placing them in the conservatorship of the Federal Housing Finance Agency, a newly created independent regulator. In addition to placing the companies in conservatorship, the U.S. Treasury announced three additional steps that it intended to take with respect to FNMA and FHLMC. First, the U.S. Treasury has entered into senior preferred stock purchase agreements (“SPSPAs”) under which, if the FHFA determines that FNMA’s or FHLMC’s liabilities have exceeded its assets under generally accepted accounting principles, the U.S. Treasury will contribute cash capital to the company in an amount equal to the difference between liabilities and assets. The SPSPAs are designed to provide protection to the senior and subordinated debt and the mortgage-backed securities issued by FNMA and FHLMC. Second, the U.S. Treasury established a new secured lending credit facility that was available to FNMA and FHLMC until December 31, 2009. Third, the U.S. Treasury initiated a temporary program to purchase FNMA and FHLMC mortgage-backed securities, which terminated on December 31, 2009. No assurance can be given that the U.S. Treasury initiatives discussed above with respect to the debt and mortgage-backed securities issued by FNMA and FHLMC will be successful, or, with respect to initiatives that have expired, that the U.S. Treasury would undertake similar initiatives in the future.

Private Mortgage Pass-Through Securities. Private mortgage pass-through securities (“private pass-throughs”) are structured similarly to the Ginnie Mae, Fannie Mae and Freddie Mac mortgage pass-through securities described above and are issued by originators of and investors in mortgage loans, including savings and loan associations, mortgage banks, commercial banks, investment banks and special purpose subsidiaries of the foregoing. Private pass-throughs are usually backed by a pool of conventional fixed rate or adjustable rate mortgage loans. Since private pass-throughs typically are not guaranteed by an entity having the credit status of GNMA, FNMA or FHLMC, such securities generally are structured with one or more types of credit enhancement. See “Types of Credit Support,” below.

most cases, on a monthly basis. CMOs may be collateralized by whole mortgage loans or private mortgage bonds, but are more typically collateralized by portfolios of mortgage pass-through securities guaranteed by GNMA, FHLMC or FNMA, and their income streams.

In a typical CMO transaction, a corporation (“issuer”) issues multiple series (e.g., A, B, C, Z) of CMO bonds (“Bonds”). Proceeds of the Bond offering are used to purchase mortgages or mortgage pass-through certificates (“Collateral”). The Collateral is pledged to a third party trustee as security for the Bonds. Principal and interest payments from the Collateral are used to pay principal on the Bonds in the order A, B, C, Z. The Series A, B and C Bonds all bear current interest. Interest on the Series Z Bond is accrued and added to principal and a like amount is paid as principal on the Series A, B or C Bond currently being paid off. When the Series A, B and C Bonds are paid in full, interest and principal on the Series Z Bond begins to be paid currently. CMOs may be less liquid and may exhibit greater price volatility than other types of mortgage- or asset-backed securities.

Mortgage TBAs. A Fund may invest in mortgage pass-through securities eligible to be sold in the “to-be-announced” or TBA market (“Mortgage TBAs”). Mortgage TBAs provide for the forward or delayed delivery of the underlying instrument with settlement up to 180 days. The term TBA comes from the fact that the specific mortgage-backed security that will be delivered to fulfill a TBA trade is not designated at the time the trade is made, but rather is generally announced 48 hours before the settlement date. To the extent a Fund purchases or sells Mortgage TBAs, the Fund is subject to the risk that the counterparty may fail to consummate the transaction, which could cause the Fund to miss the opportunity to obtain a price or yield considered to be advantageous. Mortgage TBAs may also have a leverage-like effect on a Fund and may cause a Fund to be more volatile. In addition, when a fund sells Mortgage TBAs, it incurs risks similar to those incurred in short sales. For example, when a Fund sells Mortgage TBAs without owning or having the right to obtain the deliverable securities, it incurs a risk of loss because it could have to purchase the securities at a price that is higher than the price at which it sold them. Also, a Fund may be unable to purchase the deliverable securities if the corresponding market is illiquid.

Mortgage Dollar Rolls. In a mortgage dollar roll transaction, one party sells mortgage-backed securities, principally Mortgage TBAs, for delivery in the current month and simultaneously contracts with the same counterparty to repurchase similar (same type, coupon and maturity) but not identical securities on a specified future date. During the period between the sale and repurchase in a mortgage dollar roll transaction, a Fund will not be entitled to receive interest and principal payments on securities sold. Losses may arise due to changes in the value of the securities or if the counterparty does not perform under the terms of the agreement. If the counterparty files for bankruptcy or becomes insolvent, the Fund’s right to repurchase or sell securities may be limited. Mortgage dollar rolls may be subject to leverage risks. In addition, mortgage dollar rolls may increase interest rate risk. The benefits of mortgage dollar rolls may depend upon the Adviser’s ability to predict mortgage prepayments and interest rates. There is no assurance that mortgage dollar rolls can be successfully employed.

Stripped Mortgage-Backed Securities. Stripped mortgage-backed securities (“SMBS”) are derivative multiclass mortgage securities. SMBS may be issued by agencies or instrumentalities of the U.S. Government, or by private originators of, or investors in, mortgage loans, including savings and loan associations, mortgage banks, commercial banks, investment banks and special purpose subsidiaries of the foregoing.

SMBS are usually structured with two classes that receive different proportions of the interest and principal distributions on a pool of mortgage-backed securities. A common type of SMBS will have one class receiving

some of the interest and most of the principal from the mortgage-backed securities, while the other class will receive most of the interest and the remainder of the principal. In the most extreme case, one class will receive all the interest (the interest-only or “IO” class), while the other class will receive all the principal (the principal-only or “PO” class). The yield to maturity on an IO class is extremely sensitive to the rate of principal payments (including prepayments) on the related underlying mortgage-backed securities and a rapid rate of principal payments may have a material adverse effect on a Fund’s yield to maturity. If the underlying mortgage-backed securities experience greater than anticipated prepayments of principal, a Fund may fail to fully recoup its initial investment in these securities.

Although SMBS are purchased and sold by institutional investors through several investment banking firms acting as brokers or dealers, these securities were only recently developed and, accordingly, may have less liquidity than other securities. A Fund will invest only in IO and PO class mortgage obligations collateralized by securities guaranteed by the U.S. Government.

Types of Credit Support. Mortgage-backed and asset-backed securities are often backed by a pool of assets representing the obligations of a number of different parties. To mitigate the effect of failures by obligors on underlying assets to make payments, such securities may contain elements of credit support. Such credit support falls into two categories: (i) liquidity protection and (ii) protection against losses resulting from ultimate default by an obligor on the underlying assets. Liquidity protection refers to the provision of advances, generally by the entity administering the pool of assets, to ensure that the receipt of payments on the underlying pool occurs in a timely fashion. Protection against losses resulting from ultimate default ensures ultimate payment of the obligations on at least a portion of the assets in the pool. Such protection may be provided through guarantees, insurance policies or letters of credit obtained by the issuer or sponsor from third parties, through various means of structuring the transaction or through a combination of such approaches.

Examples of credit support arising out of the structure of the transaction include “senior-subordinated securities” (multiple class securities with one or more classes subordinate to other classes as to the payment of principal thereof and interest thereon, with the result that defaults on the underlying assets are borne first by the holders of the subordinated class), creation of “reserve funds” (where cash or investments, sometimes funded from a portion of the payments on the underlying assets, are held in reserve against future losses) and “overcollateralization” (where the scheduled payments on, or the principal amount of, the underlying assets exceed that required to make payment of the securities and pay any servicing or other fees). The degree of credit support provided for each issue is generally based upon historical information respecting the level of credit risk associated with the underlying assets. Delinquency or loss in excess of that anticipated could adversely affect the return on an investment in such a security.

Asset-Backed Securities. The securitization techniques used to develop mortgage-backed securities are now being applied to a broad range of assets. Through the use of trusts and special purpose corporations, various types of assets, primarily automobile and credit card receivables, are being securitized in pass-through structures similar to the mortgage pass-through structures described above or in a pay-through structure similar to the CMO structure. A Fund, consistent with its investment objective and policies, may invest in these and other types of asset-backed securities that may be developed in the future.

As with mortgage-backed securities, the yield characteristics of asset-backed securities differ from traditional debt securities. As with mortgage-backed securities, asset-backed securities are often backed by a pool of assets representing the obligations of a number of different parties and use similar credit enhancement techniques. See “General Information on Mortgage-Backed Securities,” above. In general, however, the collateral supporting asset-backed securities is of shorter maturity than mortgage loans and is less likely to experience substantial prepayments. Although certain of the factors that affect the rate of prepayments on mortgage-backed securities also affect the rate of prepayments on asset-backed securities, during any particular period the predominant factors affecting prepayment rates on mortgage-backed securities and asset-backed securities may be different.

Asset-backed securities present certain risks that are not presented by mortgage-backed securities. Primarily, these securities do not have the benefit of the same security interest in the related collateral. Credit card receivables are generally unsecured and the debtors are entitled to the protection of a number of state and federal consumer credit laws, many of which give such debtors the right to set off certain amounts owed on the credit cards, thereby reducing the balance due. Most issuers of automobile receivables permit the servicers to retain possession of the underlying obligations. If the servicers were to sell these obligations to another party, there is a risk that the purchaser would acquire an interest superior to that of the holders of the related automobile receivables. In addition, because of the large number of vehicles involved in a typical issuance and technical requirements under state laws, the trustee for the holders of the automobile receivables may not have a proper security interest in all the obligations backing such receivables. Therefore, there is the possibility that recoveries on repossessed collateral may not, in some cases, be available to support payments on these securities.

Inverse Floaters. The Bond Fund, the Income Fund and the Low Duration Fund may invest in mortgage derivative products like inverse floating rate debt instruments (“inverse floaters”). The interest rate on an inverse floater resets in the opposite direction from the market rate of interest to which the inverse floater is indexed. The income from an inverse floater may be magnified to the extent that its rate varies by a magnitude that exceeds the magnitude of the change in the index rate of interest. The higher the degree of magnification in an inverse floater, the greater the volatility in its market value. Accordingly, the duration of an inverse floater may exceed its stated final maturity. The coupon of an inverse floating rate note moves inversely to the movement of interest rates. In addition, mortgage-backed inverse floaters will experience approximately the same changes in average lives and durations that other comparable fixed-rate mortgage-backed bonds do when prepayments rise and fall with declines and increases in interest rates. In a rising interest rate environment, the declining coupon coupled with the increase in the average life can magnify the price decline relative to a fixed-rate obligation. Conversely, rate declines increase coupon income and gradually shorten the average life, which tends to amplify the price increase. Inverse floaters are typically priced based on a matrix.

Convertible Securities. Convertible securities are bonds, notes, debentures, preferred stocks and other securities that are convertible into common stock. Investments in convertible securities can provide an opportunity for capital appreciation and/or income through interest and dividend payments by virtue of their conversion or exchange features.

The convertible securities in which the Funds may invest are either fixed income or zero coupon debt securities that may be converted or exchanged at a stated or determinable exchange ratio into underlying shares of common stock. The exchange ratio for any particular convertible security may be adjusted from time to time due to stock splits, dividends, spin-offs, other corporate distributions or scheduled changes in the exchange ratio. Convertible debt securities and convertible preferred stocks, until converted, have general characteristics similar to both debt and equity securities. Although to a lesser extent than with debt securities generally, the market value of convertible securities tends to decline as interest rates increase and, conversely, tends to increase as interest rates decline. In addition, because of the conversion or exchange feature, the market value of convertible securities typically changes as the market value of the underlying common stock changes, and, therefore, also tends to follow movements in the general market for equity securities. A unique feature of convertible securities is that as the market price of the underlying common stock declines, convertible securities tend to trade increasingly on a yield basis, and so may not experience market value declines to the same extent as the underlying common stock. When the market price of the underlying common stock increases, the prices of the convertible securities tend to rise as a reflection of the value of the underlying common stock, although typically not as much as the underlying common stock. While no securities investments are without risk, investments in convertible securities generally entail less risk than investments in common stock of the same issuer. The Bond Fund will not convert or exchange convertible securities it owns into the underlying shares of common stock.

As debt securities, convertible securities are investments that provide for a stream of income (or in the case of zero coupon securities, accretion of income) with generally higher yields than common stocks. Convertible securities generally offer lower yields than non-convertible securities of similar quality because of their conversion or exchange features.

Of course, like all debt securities, there can be no assurance of income or principal payments because the issuers of the convertible securities may default on their obligations.

Convertible securities generally are subordinated to other similar but non-convertible securities of the same issuer, although convertible bonds, as corporate debt obligations, enjoy seniority in right of payment to all equity securities, and convertible preferred stock is senior to common stock, of the same issuer. However, because of the subordination feature, convertible bonds and convertible preferred stock typically have lower ratings than similar non-convertible securities. Convertible securities may be issued as fixed income obligations that pay current income or as zero coupon notes and bonds.

Derivative Instruments. In General. The Growth Fund, Large Cap Growth Fund, Mid Cap Growth Fund, Small-Mid Cap Core Fund, Small-Mid Cap Growth Fund, Small-Mid Cap Value Fund, Small Cap Growth Fund, Small Cap Value Fund, Global Leaders Fund, International Leaders Fund, International Growth Fund, Institutional International Growth Fund, International Small Cap Growth Fund, Emerging Markets Leaders Fund, Emerging Markets Growth Fund, Emerging Markets Small Cap Growth Fund, Bond Fund, Income Fund and Low Duration Fund may use derivative instruments for the purpose of bona fide hedging or risk management as well as to equitize cash in situations involving large cash inflows or anticipated large redemptions. The Macro Allocation Fund uses derivatives as part of its principal investment strategies.

Derivative instruments are commonly defined to include securities or contracts whose values depend on (or “derive” from) the value of one or more other assets, such as securities, currencies or commodities. These “other assets” are commonly referred to as “underlying assets.” A derivative instrument generally consists of, is based upon or exhibits characteristics similar to options or forward contracts. Options and forward contracts are considered to be the basic “building blocks” of derivatives. For example, forward-based derivatives include forward contracts, swap contracts, as well as exchange-traded futures. Option-based derivatives include privately negotiated, over-the-counter (“OTC”) options (including caps, floors, collars and options on forward and swap contracts) and exchange-traded options on futures. Diverse types of derivatives may be created by combining options or forward contracts in different ways, and by applying these structures to a wide range of underlying assets.

An option is a contract in which the “holder” (the buyer) pays a certain amount (“premium”) to the “writer” (the seller) to obtain the right, but not the obligation, to buy from the writer (in a “call”) or sell to the writer (in a “put”) a specific asset at an agreed upon price at or before a certain time. The holder pays the premium at inception and has no further financial obligation. The holder of an option-based derivative generally will benefit from favorable movements in the price of the underlying asset but is not exposed to corresponding losses due to adverse movements in the value of the underlying asset. The writer of an option-based derivative generally will receive fees or premiums but generally is exposed to losses due to changes in the value of the underlying asset.

A forward is a sales contract between a buyer (holding the “long” position) and a seller (holding the “short” position) for an asset with delivery deferred until a future date. The buyer agrees to pay a fixed price at the agreed future date and the seller agrees to deliver the asset. The seller hopes that the market price on the delivery date is less than the agreed upon price, while the buyer hopes for the contrary. The change in value of a forward-based derivative generally is roughly proportional to the change in value of the underlying asset.

Hedging. The Funds may use derivative instruments to protect against possible adverse changes in the market value of securities held in, or are anticipated to be held in, its portfolio. Derivatives may also be used to “lock-in” realized but unrecognized gains in the value of its portfolio securities. Hedging strategies, if successful, can reduce the risk of loss by wholly or partially offsetting the negative effect of unfavorable price movements in the investments being hedged. However, hedging strategies can also reduce the opportunity for gain by offsetting the positive effect of favorable price movements in the hedged investments. To the extent that a hedge matures prior to or after the disposition of the investment subject to the hedge, any gain or loss on the hedge will be realized earlier or later than any offsetting gain or loss on the hedged investment.

Managing Risk. The Funds may also use derivative instruments to manage the risks of its portfolio. Risk management strategies include, but are not limited to, facilitating the sale of portfolio securities, managing the effective maturity or duration of debt obligations in its portfolio, establishing a position in the derivatives markets as a substitute for buying or selling certain securities, or creating or altering exposure to certain asset classes, such as equity, debt or foreign securities. The use of derivative instruments may provide a less expensive, more expedient or more specifically focused way to invest than “traditional” securities (i.e., stocks or bonds) would.

Exchange and OTC Derivatives. Derivative instruments may be exchange-traded or traded in OTC transactions between private parties. Exchange-traded derivatives are standardized derivatives contracts traded on a regulated exchange. Exchange contracts are generally very liquid. The exchange clearinghouse is the counterparty of every contract. Thus, each holder of an exchange contract bears the credit risk of the clearinghouse (and has the benefit of its financial strength) rather than that of a particular counterparty. OTC transactions are subject to additional risks, such as the credit risk of the counterparty to the instrument, and are less liquid than exchange-traded derivatives since they often can only be closed out with the other party to the transaction.

Risks and Special Considerations. The use of derivative instruments involves risks and special considerations as described below. Risks pertaining to particular derivative instruments are described in the sections that follow.

(1) Market Risk. The primary risk of derivatives is the same as the risk of the underlying assets, namely that the value of the underlying asset may go up or down. Adverse movements in the value of an underlying asset can expose the Funds to losses. Derivative instruments may include elements of leverage and, accordingly, the fluctuation of the value of the derivative instrument in relation to the underlying asset may be magnified. The successful use of derivative instruments depends upon a variety of factors, particularly the ability to predict movements of the securities, currencies and commodity markets, which requires different skills than predicting changes in the prices of individual securities. There can be no assurance that any particular strategy adopted will succeed.

(2) Counterparty Risk. The Funds will be subject to the risk that a loss may be sustained as a result of the failure of a counterparty to comply with the terms of a derivative instrument. The counterparty risk for exchange-traded derivative instruments is generally less than for privately negotiated or OTC derivative instruments, since generally a clearing agency, which is the issuer or counterparty to each exchange-traded instrument, provides a guarantee of performance. For privately negotiated instruments, there is no similar clearing agency guarantee. In all transactions, the Funds will bear the risk that the counterparty will default, and this could result in a loss of the expected benefit of the derivative transaction and possibly other losses.

(3) Contractual Default and Cross-Default Risk. A default by a Fund under a contract with any single counterparty (or the subsequent termination of such contract), in addition to triggering rights and remedies in favor of the counterparty, may result in or constitute a default by the Fund under other contracts with that counterparty (or any of its affiliates) and/or with other counterparties. Any default by a Fund under one of its contracts and any action taken by one or more counterparties following the Fund’s default could adversely affect the Fund and its investing activities.

(4) Correlation Risk. When a derivative transaction is used to hedge another position, changes in the market value of the combined position (the derivative instrument plus the position being hedged) result from an imperfect correlation between the price movements of the two instruments. With a perfect hedge, the value of the combined position remains unchanged for any change in the price of the underlying asset. With an imperfect hedge, the values of the derivative instrument and the hedged position are not perfectly correlated. Correlation risk is the risk that there might be imperfect correlation, or even no correlation, between price movements of a derivative instrument and price movements of investments being hedged. For example, if the value of a derivative instrument used in a short hedge (such as writing a call option, buying a put option or selling a futures contract) increased by less than the decline in value of the hedged investments, the hedge would not be perfectly

correlated. Such a lack of correlation might occur due to factors unrelated to the value of the investments being hedged, such as speculative or other pressures on the markets in which these instruments are traded. The effectiveness of hedges using instruments on indices will depend, in part, on the degree of correlation between price movements in the index and price movements in the investments being hedged.

(5) Liquidity Risk. Derivatives are also subject to liquidity risk. Liquidity risk is the risk that a derivative instrument cannot be sold, closed out or replaced quickly at or very close to its fundamental value. Generally, exchange-traded derivatives are very liquid because the exchange clearinghouse is the counterparty of every contract. OTC derivatives are less liquid than exchange-traded derivatives since they often can be closed out only with the other party to the transaction. The Funds might be required by applicable regulatory requirements to maintain assets as “cover,” maintain segregated accounts and/or make margin payments when they take positions in derivative instruments involving obligations to third parties (i.e., instruments other than purchased options). If the Funds were unable to close out their positions in such instruments, they might be required to continue to maintain such assets or accounts or make such payments until the position expired, matured or was closed out. The requirements might impair the Funds’ ability to sell a portfolio security or make an investment at a time when it would otherwise be favorable to do so, or require that the Funds sell a portfolio security at a disadvantageous time. The Funds’ ability to sell or close out a position in an instrument prior to expiration or maturity depends on the existence of a liquid secondary market or, in the absence of such a market, the ability and willingness of the counterparty to enter into a transaction closing out the position. Therefore, there is no assurance that any derivatives position can be sold or closed out at a time and price that is favorable to the Funds.

(6) Legal Risk. Legal risk is the risk of loss caused by the legal unenforceability of a party’s obligations under the derivative. While a party seeking price certainty agrees to surrender the potential upside gain in exchange for downside protection, the party taking the risk is looking for a positive payoff. Despite this voluntary assumption of risk, a counterparty that has lost money in a derivative transaction may try to avoid payment by exploiting various legal uncertainties about certain derivative products.

(7) Systemic or “Interconnection” Risk. Interconnection risk is the risk that a disruption in the financial markets will cause difficulties for all market participants. In other words, a disruption in one market will spill over into other markets, perhaps creating a chain reaction. Much of the OTC derivatives market takes place among the OTC dealers themselves, thus creating a large interconnected web of financial obligations. This interconnectedness raises the possibility that a default by one large dealer could create losses at other dealers and destabilize the entire market for OTC derivative instruments.

(8) Regulatory Risk. It is possible that government regulation of the use of derivatives by mutual funds or of various types of derivative instruments, including futures, options and swap agreements, may limit or prevent a Fund from using derivatives as a part of its investment strategies. Limits or restrictions applicable to the counterparties with which a Fund engages in derivative transactions could also prevent the Fund from using certain derivatives.

For the Macro Allocation Fund, unfavorable regulatory developments could ultimately prevent the Fund from being able to implement its investment strategies. It is impossible to predict the effects of future legislation and regulation in this area, but the effects could be substantial and adverse. It is possible that legislative and regulatory activity could limit or restrict the ability of the Fund to use certain derivatives as a part of its investment strategies and could alter, perhaps to a material extent, the nature of an investment in the Fund or the ability of the Fund to continue to implement its investment strategies.

transactions in the United States is a changing area of law and is subject to modification by government and judicial action.

In particular, the Dodd-Frank Wall Street Reform and Consumer Protection Act (the “Dodd-Frank Act”) was signed into law on July 21, 2010. The Dodd-Frank Act changed the way in which the U.S. financial system is supervised and regulated. Title VII of the Dodd-Frank Act sets forth a legislative framework for OTC derivatives, including financial instruments, such as swaps, in which a Fund may invest. Title VII of the Dodd-Frank Act made broad changes to the OTC derivatives market, grants significant authority to the SEC, the CFTC and other federal regulators to regulate OTC derivatives and market participants, and requires clearing and exchange trading of many OTC derivatives transactions. The CFTC and the SEC finalized the definition of “swap” and “security-based swap” and provided parameters around which contracts will be subject to further regulation under the Dodd-Frank Act.

Provisions in the Dodd-Frank Act include new capital and margin requirements and the mandatory use of clearinghouse mechanisms for many OTC derivative transactions. The CFTC, SEC and other federal regulators have been tasked with developing the rules and regulations enacting the provisions of the Dodd-Frank Act. While certain of the rules are now effective, other rules are not yet final, so it is not possible at this time to gauge the exact nature and scope of the impact of the Dodd-Frank Act on the Fund.

Wholly Owned Subsidiary. To the extent the Macro Allocation Fund seeks to invest in commodities, the Fund may gain exposure to the commodity markets by investing a portion of its assets in William Blair MAS Ltd., a wholly owned subsidiary of the Fund organized under the laws of the Cayman Islands (the “Subsidiary”), which is expected to invest mainly in commodity-linked derivative instruments, such as futures or swaps. The Subsidiary may also hold fixed income securities, some of which may serve as margin or collateral for the Subsidiary’s derivative positions. Investments in the Subsidiary are expected to provide exposure to the commodity markets within the limitations of Subchapter M of the Internal Revenue Code of 1986, as amended (the “Code”) (see the “General Trust Information—Federal Income Tax Matters” section).

To the extent that the Fund invests in its Subsidiary, the Fund will be subject to the risks associated with the derivative instruments invested in by the Subsidiary. The Subsidiary is not registered under the 1940 Act and is not subject to the investor protections of the 1940 Act and other U.S. regulations. Changes in the laws of the U.S. and/or the Cayman Islands could result in the inability of the Fund and/or its Subsidiary to operate as intended, and could adversely affect the Fund and its shareholders. As of the date of this Statement of Additional Information, the Subsidiary is not operational and the Fund is not currently investing in the Subsidiary.

In order to qualify for the special tax treatment accorded regulated investment companies and their shareholders under the Code, the Fund must, among other things, satisfy certain diversification requirements, including the requirement that not more than 25% of the value of the Fund’s total assets may be invested in the securities (other than those of the U.S. government or other regulated investment companies) of any one issuer or of two or more issuers which the Fund controls and which are engaged in the same, similar or related trades or businesses. Therefore, so long as the Fund is subject to this limit, the Fund may not invest any more than 25% of the value of its total assets in the Subsidiary. In addition, in order to qualify for the special tax treatment accorded regulated investment companies and their shareholders under the Code, the Fund must, among other things, derive at least 90% of its gross income from certain specified sources (“qualifying income”). Income from certain commodity and commodity-linked derivatives does not constitute qualifying income to the Fund. The tax treatment of commodity-linked notes and certain other derivative instruments in which the Fund might invest is not certain, in particular with respect to whether income and gains from such instruments constitute qualifying income. If the Fund treats income from a particular instrument as qualifying income and the income is later determined not to constitute qualifying income, and, together with any other non-qualifying income, causes the Fund’s non-qualifying income to exceed 10% of its gross income in any taxable year, the Fund will fail to qualify as a regulated investment company unless it is eligible to and does pay a tax at the fund level.

General Limitations on Derivatives. The use of derivative instruments is subject to applicable regulations of the SEC, the several options and futures exchanges upon which they may be traded, the CFTC and various state regulatory authorities. In addition, the Funds’ ability to use derivative instruments may be limited by certain tax considerations. Effective December 31, 2012, the CFTC adopted certain regulatory changes that subject registered investment companies and advisers to regulation by the CFTC if a fund invests more than a prescribed level of its liquidation value in CFTC-regulated futures, options and swaps, or if the fund markets itself as providing investment exposure to such instruments. To the extent the Funds except the Macro Allocation Fund use CFTC-regulated futures, options and swaps, they intend to do so below such prescribed levels and will not market themselves as “commodity pools” or vehicles for trading such instruments. Accordingly, the Adviser has claimed an exclusion from the definition of the term “commodity pool operator” with respect to each Fund except the Macro Allocation Fund under the Commodity Exchange Act (“CEA”) pursuant to Rule 4.5 under the CEA. The Adviser is not, therefore, subject to registration or regulation as a “commodity pool operator” with respect to the Funds other than the Macro Allocation Fund under the CEA.

The Adviser will act as a “commodity pool operator” with respect to the operation of the Macro Allocation Fund and its Subsidiary and is registered with the National Futures Association with respect to the Fund. As a result, the Adviser is subject to dual regulation by the CFTC and the SEC with respect to the Fund. The CFTC adopted regulations that seek to “harmonize” CFTC regulations with overlapping SEC rules and regulations. The Adviser has availed itself of the CFTC’s substitute compliance option under the harmonization regulations with respect to the Fund by filing a notice with the National Futures Association. The Adviser will remain subject to certain CFTC-mandated disclosure, reporting and recordkeeping regulations. Compliance with the CFTC regulations could increase the Fund’s expenses, adversely affecting investment returns.

Certain derivatives transactions expose a Fund to an obligation to make future payments to third parties. Examples of these types of transactions, include, but are not limited to, derivatives such as swaps, futures, forwards, and options.

In order for a Fund not to consider certain derivatives transactions borrowings under the 1940 Act, the Fund will either (1) segregate cash or liquid assets or (2) otherwise “cover” its future obligations under the transactions such as by holding an offsetting investment. The amount that needs to be segregated for a particular derivative investment will vary by investment. A Fund may be required to segregate the entire value of the investment or the daily net (mark-to-market) obligation. To the extent a Fund is only required to segregate the daily mark-to-market obligation, the Fund will have the ability to employ leverage to a greater extent than if it set aside cash or other liquid assets equal to the notional amount of the contract, which may increase the risk associated with such transactions.

Assets used as segregation or “cover” cannot be sold while the position in the corresponding transaction is open, unless they are replaced with other appropriate assets. As a result, the commitment of a large portion of the Fund’s assets for segregation and “cover” purposes could impede portfolio management or the Fund’s ability to meet redemption requests or other current obligations. Segregating assets or otherwise “covering” for these purposes does not necessarily limit the percentage of the assets of the Fund that may be at risk with respect to certain derivative transactions.

In November 2019, the SEC published a proposed rulemaking related to the use of derivatives and certain other transactions by registered investment companies that would, if adopted, for the most part rescind the guidance of the SEC and its staff regarding asset segregation and cover transactions. Instead of complying with current guidance, a Fund would need to trade derivatives and other transactions that create future payment or delivery obligations (except reverse repurchase agreements and similar financing transactions) subject to a value-at-risk leverage limit, certain other derivatives risk management program and testing requirements and requirements related to board and SEC reporting. These new requirements would apply unless a Fund qualified as a “limited derivatives user,” as defined in the SEC’s proposal. Any new requirements, if adopted, may increase the cost of a Fund’s investments and cost of doing business, which could adversely affect investors.

Options. An option is a contract in which the “holder” (the buyer) pays a certain amount (“premium”) to the “writer” (the seller) to obtain the right, but not the obligation, to buy from the writer (in a “call”) or sell to the writer (in a “put”) a specific asset at an agreed upon price (“strike price” or “exercise price”) at or before a certain time (“expiration date”). The holder pays the premium at inception and has no further financial obligation. The holder of an option will benefit from favorable movements in the price of the underlying asset but is not exposed to corresponding losses due to adverse movements in the value of the underlying asset. The writer of an option will receive fees or premiums but is exposed to losses due to changes in the value of the underlying asset. The Funds may buy or write (sell) put and call options on assets, such as securities, currencies, futures, commodities, commodities indices and indices of debt and equity securities and enter into closing transactions with respect to such options to terminate an existing position. Options used by the Funds may include European, American and Bermuda style options. If an option is exercisable only at maturity, it is a “European” option; if it is also exercisable prior to maturity, it is an “American” option. If it is exercisable only at certain times, it is a “Bermuda” option.

The purchase of a call option serves as a long position, and the purchase of a put option serves as a short position. Writing put or call options can enable the Funds to enhance income by reason of the premiums paid by the purchaser of such options. If a Fund uses options for hedging purposes, writing call options may serve as a limited short hedge because declines in the value of the hedged investment would be offset to the extent of the premium received for writing the option. However, if the security appreciates to a price higher than the exercise price of the call option, it can be expected that the option will be exercised and the Funds will be obligated to sell the security at less than its market value or will be obligated to purchase the security at a price greater than that at which the security must be sold under the option. All or a portion of any assets used as cover for OTC options written by the Funds could be considered illiquid. Writing put options may serve as a limited long hedge because decreases in the value of the hedged investment would be offset to the extent of the premium received for writing the option. However, if the security depreciates to a price lower than the exercise price of the put option, it can be expected that the put option will be exercised and the Funds will be obligated to purchase the security at more than its market value.

The value of an option position will reflect, among other things, the historical price volatility of the underlying investment, the current market value of the underlying investment, the time remaining until expiration, the relationship of the exercise price to the market price of the underlying investment, and general market conditions.

The Funds may effectively terminate a right or obligation under an option by entering into a closing transaction. For example, the Funds may terminate an obligation under a call or put option that they had written by purchasing an identical call or put option; this is known as a closing purchase transaction. Conversely, the Funds may terminate a position in a put or call option they had purchased by writing an identical put or call option; this is known as a closing sale transaction. Closing transactions permit the Funds to realize the profit or limit the loss on an option position prior to its exercise or expiration.

The Funds may purchase or write both exchange-traded and OTC options. Exchange-traded options are issued by a clearing organization affiliated with the exchange on which the option is listed that, in effect, guarantees completion of every exchange-traded option transaction. In contrast, OTC options are contracts between the Funds and the other party to the transaction (“counterparty”) (usually a securities dealer or a bank) with no clearing organization guarantee. Thus, when the Funds purchase or write an OTC option, they rely on the counterparty to make or take delivery of the underlying investment upon exercise of the option. Failure by the counterparty to do so would result in the loss of any premium paid by the Funds as well as the loss of any expected benefit of the transaction.

The Funds’ ability to establish and close out positions in exchange-listed options depends on the existence of a liquid market. The Funds intend to purchase or write only those exchange-traded options for which there appears to be a liquid secondary market. However, there can be no assurance that such a market will exist at any particular time. Closing transactions can be made for OTC options only by negotiating directly with the

counterparty, or by a transaction in the secondary market if any such market exists. Although the Funds will enter into OTC options only with counterparties that are expected to be capable of entering into closing transactions with the Funds, there is no assurance that the Funds will in fact be able to close out an OTC option at a favorable price prior to expiration. In the event of insolvency of the counterparty, the Funds might be unable to close out an OTC option position at any time prior to its expiration. If the Funds were unable to effect a closing transaction for an option it had purchased, it would have to exercise the option to realize any profit.

The Funds also may engage in options transactions as described above on securities indices and other financial or commodities indices and, in so doing, can achieve many of the same objectives they would achieve through the sale or purchase of options on individual securities or other instruments. Options on securities indices and other financial or commodities indices are similar to options on a security or other instrument except that, rather than settling by physical delivery of the underlying instrument, they settle by cash settlement, i.e., an option on an index gives the holder the right to receive, upon exercise of the option, an amount of cash if the closing level of the index upon which the option is based exceeds, in the case of a call, or is less than, in the case of a put, the exercise price of the option (except if, in the case of an OTC option, physical delivery is specified). This amount of cash is equal to the excess of the closing price of the index over the exercise price of the option, which also may be multiplied by a formula value. The seller of the option is obligated, in return for the premium received, to make delivery of this amount. The gain or loss on an option on an index depends on price movements in the instruments making up the market, market segment, industry or other composite on which the underlying index is based, rather than price movements in individual securities, as is the case with respect to options on securities.

The writing and purchasing of options is a highly specialized activity that involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. Imperfect correlation between the options and securities markets may detract from their effectiveness.

Futures Contracts. The Funds may enter into contracts for the purchase or sale for future delivery of equity or fixed income securities, foreign currencies and contracts based on financial indices, including indices of U.S. Government securities or equity or foreign government securities, or commodities. The Funds may also purchase put and call options, and write covered put and call options, on futures in which they are allowed to invest. If a Fund uses futures for hedging purposes, the purchase of futures or call options thereon may serve as a long hedge, and the sale of futures or the purchase of put options thereon may serve as a short hedge. Writing covered call options on futures contracts can serve as a limited short hedge, and writing covered put options on futures contracts can serve as a limited long hedge, using a strategy similar to that used for writing covered options in securities. The Funds may also write put options on futures contracts while at the same time purchasing call options on the same futures contracts in order to create synthetically a long futures contract position. Such options would have the same strike prices and expiration dates.

Each Fund except the Macro Allocation Fund uses futures contracts primarily for the purpose of bona fide hedging or risk management. Each such Fund may, however, use futures contracts to equitize cash as well, particularly in situations involving large cash inflows or anticipated large redemptions. For each Fund except the Macro Allocation Fund, a Fund’s primary purpose in entering into futures contracts is to protect that Fund from fluctuations in the value of securities or interest rates without actually buying or selling the underlying debt or equity security. For example, if a Fund anticipates an increase in the price of stocks, and it intends to purchase stocks at a later time, that Fund could enter into a futures contract based upon a stock index as a temporary substitute for stock purchases. If an increase in the market occurs that influences the stock index, as anticipated, the value of the futures contracts will increase, thereby serving as a hedge against that Fund not participating in a market advance. Conversely, if a Fund holds stocks and seeks to protect itself from a decrease in stock prices, the Fund might sell stock index futures contracts, thereby hoping to offset the potential decline in the value of its portfolio securities by a corresponding increase in the value of the futures contract position. A Fund could protect against a decline in stock prices by selling portfolio securities and investing in money market instruments, but the use of futures contracts enables it to maintain a defensive position without having to sell portfolio securities. Although techniques other than sales and purchases of futures contracts could be used to reduce the Funds’

exposure to market or interest rate fluctuations, the Funds may be able to hedge their exposure more effectively and perhaps at a lower cost through the use of futures contracts.

A futures contract provides for the future sale by one party and purchase by another party of a specified amount of a specific financial instrument, index, security or commodity for a specified price at a designated date, time and place. An index futures contract is an agreement pursuant to which the parties agree to take or make delivery of an amount of cash equal to the difference between the value of the index at the close of the last trading day of the contract and the price at which the index futures contract was originally written. Transaction costs are incurred when a futures contract is bought or sold and margin deposits must be maintained. A futures contract may be satisfied by delivery or purchase, as the case may be, of the instrument, security or commodity or by payment of the change in the cash value of the index. More commonly, futures contracts are closed out prior to delivery by entering into an offsetting transaction in a matching futures contract. Although the value of an index might be a function of the value of certain specified securities, no physical delivery of those securities is made. If the offsetting purchase price is less than the original sale price, the Funds realize a gain; if it is more, the Funds realize a loss. Conversely, if the offsetting sale price is more than the original purchase price, the Funds realize a gain; if it is less, the Funds realize a loss. The transaction costs must also be included in these calculations. There can be no assurance, however, that the Funds will be able to enter into an offsetting transaction with respect to a particular futures contract at a particular time. If the Funds are not able to enter into an offsetting transaction, the Funds will continue to be required to maintain the margin deposits on the futures contract.

No price is paid by the Funds upon entering into a futures contract. Instead, at the inception of a futures contract, the Funds are required to deposit in a segregated account with its custodian, in the name of the futures broker through whom the transaction was effected, “initial margin” consisting of cash and/or other appropriate liquid assets in an amount generally equal to 10% or less of the contract value. Margin must also be deposited when writing a call or put option on a futures contract, in accordance with applicable exchange rules. Unlike margin in securities transactions, initial margin on futures contracts does not represent a borrowing, but rather is in the nature of a performance bond or good-faith deposit that is returned to the Funds at the termination of the transaction if all contractual obligations have been satisfied. Under certain circumstances, such as periods of high volatility, the Funds may be required by an exchange to increase the level of their initial margin payment, and initial margin requirements might be increased generally in the future by regulatory action.

Subsequent “variation margin” payments are made to and from the futures broker daily as the value of the futures position varies, a process known as “marking to market.” Variation margin does not involve borrowing, but rather represents a daily settlement of the Funds’ obligations to or from a futures broker. When a Fund purchases an option on a future, the premium paid plus transaction costs is all that is at risk. In contrast, when a Fund purchases or sells a futures contract or writes a call or put option thereon, it is subject to daily variation margin calls that could be substantial in the event of adverse price movements. If the Funds have insufficient cash to meet daily variation margin requirements, they might need to sell securities at a time when such sales are disadvantageous. Purchasers and sellers of futures positions and options on futures can enter into offsetting closing transactions by selling or purchasing, respectively, an instrument identical to the instrument held or written. Positions in futures and options on futures may be closed only on an exchange or board of trade that provides a secondary market. The Funds intend to enter into futures transactions only on exchanges or boards of trade where there appears to be a liquid secondary market. However, there can be no assurance that such a market will exist for a particular contract at a particular time.

Under certain circumstances, futures exchanges may establish daily limits on the amount that the price of a future or option on a futures contract can vary from the previous day’s settlement price; once that limit is reached, no trades may be made that day at a price beyond the limit. Daily price limits do not limit potential losses because prices could move to the daily limit for several consecutive days with little or no trading, thereby preventing liquidation of unfavorable positions.

If the Funds were unable to liquidate a futures or option on a futures contract position due to the absence of a liquid secondary market or the imposition of price limits, they could incur substantial losses. The Funds would

continue to be subject to market risk with respect to the position. In addition, except in the case of purchased options, the Funds would continue to be required to make daily variation margin payments and might be required to maintain the position being hedged by the future or option or to maintain cash or securities in a segregated account.

Certain characteristics of the futures market might increase the risk that movements in the prices of futures contracts or options on futures contracts might not correlate perfectly with movements in the prices of the underlying investments. For example, all participants in the futures and options on futures contracts markets are subject to daily variation margin calls and might be compelled to liquidate futures or options on futures contracts positions whose prices are moving unfavorably to avoid being subject to further calls. These liquidations could increase price volatility of the instruments and distort the normal price relationship between the futures or options and the underlying investments. Also, because initial margin deposit requirements in the futures markets are less onerous than margin requirements in the securities markets, there might be increased participation by speculators in the future markets. This participation also might cause temporary price distortions. In addition, activities of large traders in both the futures and securities markets involving arbitrage, “program trading” and other investment strategies might result in temporary price distortions.

Swap Agreements. Swap agreements include total return, interest rate, securities index, commodity, security, currency exchange rate, credit default, variance and volatility swaps and related caps, floors and collars. Each Fund except the Macro Allocation Fund will use such instruments solely for the purpose of bona fide hedging or risk management, such as for the purpose of attempting to obtain or preserve a particular desired return or spread at a lower cost to the Funds than if the Funds had invested directly in an instrument that yielded that desired return or spread. The Funds also may enter into swaps in order to protect against an increase in the price of, or the currency exchange rate applicable to, securities that the Funds anticipate purchasing at a later date. The Macro Allocation Fund may use swaps as part of its principal investment strategies. Cleared swaps are transacted through futures commission merchants that are members of central clearinghouses with the clearinghouse serving as a central counterparty similar to transactions in futures contracts (see additional disclosure below regarding recent requirements under the Dodd-Frank Act for the clearing of swaps). In a standard “swap” transaction, two parties agree to exchange the returns (or differentials in rates of return) earned or realized on particular predetermined investments or instruments. The gross returns to be exchanged or “swapped” between the parties are calculated with respect to a “notional amount” (e.g., the change in the value of a particular dollar amount invested at a particular interest rate, in a particular foreign currency, or in a “basket” of securities representing a particular index). Swap agreements may include caps, under which, in return for a premium, one party agrees to make payments to the other to the extent that a specified index exceeds a specified rate or amount, or “cap”; floors, under which, in return for a premium, one party agrees to make payments to the other to the extent that a specified index falls below a specified level, or “floor”; and collars, under which a party sells a cap and purchases a floor, or vice versa, in an attempt to protect itself against movements in interest or values exceeding given minimum or maximum levels. The amount of a Fund’s potential gain or loss on any swap transaction is not subject to any fixed limit. Nor is there any fixed limit on a Fund’s potential loss if it sells a cap or collar. If a Fund buys a cap, floor or collar, however, the Fund’s potential loss is limited to the amount of the fee that it has paid. When measured against the initial amount of cash required to initiate the transaction, which is typically zero in the case of most conventional swap transactions, swaps, caps, floors and collars tend to be more volatile than many other types of instruments.

The “notional amount” of a swap agreement is the agreed upon basis for calculating the obligations that the parties to a swap agreement have agreed to exchange. Under most swap agreements entered into by the Funds, the obligations of the parties would be exchanged on a “net basis.” Consequently, a Fund’s obligation (or rights) under a swap agreement will generally be equal only to the net amount to be paid or received under the agreement based on the relative values of the positions held by each party to the agreement. A Fund’s obligation under a swap agreement will be accrued daily (offset against amounts owed to the Fund) and any accrued but unpaid net amounts owed to a swap counterparty will be covered by segregating cash and/or other appropriate liquid assets.

Whether a Fund’s use of swap agreements will be successful depends, in part, on the Adviser’s ability to predict correctly whether certain types of investments are likely to produce greater returns than other investments. Moreover, a Fund bears the risk of loss of the amount expected to be received under a swap agreement in the event of the default or bankruptcy of a swap agreement counterparty. The Funds will enter into swap agreements only with counterparties that the Adviser reasonably believes are capable of performing under the swap agreements. If there is a default by the other party to such a transaction, a Fund will have to rely on its contractual remedies (which may be limited by bankruptcy, insolvency or similar laws) pursuant to the agreements related to the transaction. Certain restrictions imposed on a Fund by the Code also may limit the Fund’s ability to use swap agreements.

The swap market has grown substantially in recent years with a large number of banking firms acting as both principals and agents using standardized swap documentation. As a result, the swap market has become relatively liquid. However, swap agreements may still be subject to liquidity risk, which exists when a particular swap is difficult to purchase or sell. If a swap transaction is particularly large or if the relevant market is illiquid (as is the case with many OTC swaps), it may not be possible to initiate a transaction or liquidate a position at an advantageous time or price, which may result in significant losses. Caps, floors and collars are more recent innovations for which standardized documentation has not been fully developed and, accordingly, swaps with these features are less liquid.

The swaps market was largely unregulated prior to the enactment of the Dodd-Frank Act. Among other things, the Dodd-Frank Act sets forth a new regulatory framework for certain OTC derivatives, such as swaps and security-based swaps (referred to collectively as “swaps”), in which the Funds may be authorized to invest. The Dodd-Frank Act requires many swap transactions to be executed on registered exchanges or through swap execution facilities, cleared through a regulated clearinghouse and publicly reported. In addition, many market participants are now regulated as swap dealers or major swap participants and are, or will be, subject to certain minimum capital and margin requirements and business conduct standards. The statutory requirements of the Dodd-Frank Act are being implemented primarily through rules and regulations adopted by the SEC, the CFTC, and/or the prudential regulators (described below). The CFTC is responsible for the regulation of most swaps, and has completed most of its rules implementing the Dodd-Frank Act swap regulations. The SEC has jurisdiction over a small segment of the market referred to as “security-based swaps,” which includes swaps on single securities or credits, or narrow-based indices of securities or credits. Other federal regulators, including the US Federal Reserve Bank, the US Office of the Comptroller of Currency, the US Federal Deposit Insurance Corporation, the US Farm Credit Administration and the US Federal Housing Finance Authority (collectively, “prudential regulators”) are responsible for adopting rules establishing capital and margin requirements for swap dealers and major swap participants for which there exists an applicable prudential regulator.

As of the date of this SAI, central clearing is required only for certain market participants trading certain swaps, although central clearing for additional swaps is expected to be implemented by the CFTC until the majority of the swaps market is ultimately subject to central clearing. In addition, uncleared OTC swaps will be subject to regulatory collateral requirements that could adversely affect a Fund’s ability to enter into swaps in the OTC market. The CFTC, the prudential regulators and the SEC have each completed rulemakings under the Dodd-Frank Act on margin for uncleared OTC swaps (and option agreements that qualify as swaps). The CFTC and prudential regulator variation margin requirements went into effect for the largest swap entities in September 2016, and went into effect for financial end users in March 2017. The CFTC and prudential regulator initial margin requirements, and the SEC variation and initial margin requirements, will likely come into effect in 2021. Under these regulations, swap dealers (such as sell-side counterparties to swaps), major swap participants, and financial end users (such as buy-side counterparties to swaps who are not physical traders) are required in most instances, to post and collect initial and variation margin for their OTC swaps, depending on the regulatory classification of their counterparty. As a result of these requirements, additional capital will be required to be committed to the margin accounts to support transactions involving uncleared OTC swaps and, consequently, these transactions may become more expensive. These developments could adversely impact the profitability (if any) to the Funds from entering into these transactions.

Until the mandated rulemaking and regulations are implemented completely, it will not be possible to determine the complete impact of the Dodd-Frank Act and related regulations on a Fund, and the establishment of a centralized exchange or market for swap transactions may not result in swaps being easier to value or trade. However, it is expected that swap dealers, major market participants and swap counterparties will experience other new and/or additional regulations, requirements, compliance burdens and associated costs. Future legislation and rules may exert a negative effect on a Fund, either through limits or requirements imposed on the Fund or its counterparties. The swap market could be disrupted or limited as a result of the legislation, and the new requirements may increase the cost of a Fund’s investments and of doing business, which could adversely affect the Fund’s ability to buy or sell OTC derivatives.

Additional information about certain swap agreements that the Funds may be authorized to utilize is provided below.

Total Return Swaps. A total return swap is a contract whereby two parties agree to make payments to each other based on the positive or negative performance of an underlying asset (e.g., security, index or other financial instrument). The payments to be made in connection with a total return swap are calculated with respect to a “notional amount” (i.e., the change in the value of a particular dollar amount invested in the underlying asset). In certain total return swaps, the other party to the contract agrees to make a series of payments calculated by reference to an interest rate and/or some other agreed-upon amount.

Interest Rate Swaps. Interest rate swaps involve a commitment between parties to pay either a fixed interest rate or a floating interest rate based on a notional amount of principal. The parties make payments at predetermined intervals throughout the life of the swap. As a payer, a Fund would make the fixed payment and receive the floating payment. As a receiver, a Fund would make the floating payment and receive the fixed payment.

Credit Default Swaps. The Bond Fund, the Income Fund, the Low Duration Fund and the Macro Allocation Fund may enter into credit default swaps. A credit default swap is a contract between a buyer and a seller of protection against a pre-defined credit event (e.g., a ratings downgrade or default) on an underlying reference obligation, which may be a single debt instrument or baskets or indices of securities. Credit default swaps are used as a means of “buying” credit protection (i.e., attempting to mitigate the risk of default or credit quality deterioration in some portion of a Fund’s holdings) or “selling” credit protection (i.e., attempting to gain exposure to an underlying issuer’s credit quality characteristics without directly investing in that issuer). A Fund may be a buyer or seller of a credit default swap. Where a Fund is a seller of credit protection, it adds leverage to its portfolio because the Fund is subject to investment exposure on the notional amount of the swap which would be offset to the extent of its uncommitted cash or cash equivalents. A Fund will cover the full notional value of any credit default swap it sells. A Fund will only sell credit protection with respect to securities in which it would be authorized to invest directly.

If a Fund is a buyer of a credit default swap and no credit event occurs, a Fund will lose its premium payment and recover nothing. However, if a Fund is a buyer and a credit event occurs, a Fund will receive the full notional amount, or “par value,” of the reference obligation in exchange for the reference obligation or a payment equal to the difference in value between the full notional amount, or “par value,” of the reference obligation and the market value of the reference obligation. As a seller, a Fund receives a fixed rate of income reflecting the buyer’s premium payments through the term of the contract (typically between six months and three years), provided that there is no credit event. If a credit event occurs, a Fund must pay the buyer the full notional amount, or “par value,” of the reference obligation in exchange for the reference obligation or the difference in value between the full notional amount, or “par value,” of the reference obligation and the market value of the reference obligation. Credit default swaps may involve greater risks than if a Fund had invested in the reference obligation directly. In addition to the risks applicable to derivatives generally, credit default swaps involve special risks because they may be difficult to value and may be more susceptible to liquidity and credit risk.

Variance and Volatility Swaps. The Macro Allocation Fund may enter into variance and volatility swaps. A variance swap is an agreement between two parties to exchange cash flows based on the measured variance (or

square of volatility) of a specified underlying asset. One party agrees to exchange a “fixed rate” or strike price payment for the “floating rate” or realized price variance on the underlying asset with respect to the notional amount. At inception, the strike price chosen is generally fixed at a level such that the fair value of the swap is zero. As a result, no money changes hands at the initiation of the contract. At the expiration date, the amount paid by one party to the other is the difference between the realized price variance of the underlying asset and the strike price multiplied by the notional amount. A receiver of the realized price variance would receive a payment when the realized price variance of the underlying asset is greater than the strike price and would make a payment when that variance is less than the strike price. A payer of the realized price variance would make a payment when the realized price variance of the underlying asset is greater than the strike price and would receive a payment when that variance is less than the strike price. This type of agreement is essentially a forward contract on the future realized price variance of the underlying asset. A volatility swap is an agreement between two parties to make payments based on changes in the volatility of a specified underlying asset over a stated period of time. Specifically, one party will be required to make a payment to the other party if the volatility of the specified underlying asset increases over an agreed upon period of time, but will be entitled to receive a payment from the other party if the volatility decreases over that time period.

Additional Derivative Instruments and Strategies. In addition to the derivative instruments and strategies described above and in the Prospectus, the Adviser expects additional derivative instruments and other hedging or risk management techniques to develop from time to time. The Adviser may utilize these new derivative instruments and techniques to the extent that they are consistent with the Funds’ investment objective and permitted by the Funds’ investment limitations, operating policies and applicable regulatory authorities.

Equity Securities. Equity securities include common stocks, preferred stocks and securities convertible into common stocks. Common stock represents an ownership interest in a company. Preferred stock has a preference over common stock in liquidation, but is subordinated to the liabilities of the issuer in all respects. Preferred stock may offer the opportunity for capital appreciation as well as periodic income. The value of the equity securities the Fund holds may decrease in response to the activities of an individual company or in response to general market, business and economic conditions. If this occurs, the Fund’s share price may also decrease. In addition, there is the risk that individual securities may not perform as expected.

Exchange-Traded Notes. The Macro Allocation Fund may invest in exchange traded notes (“ETNs”). ETNs are securities that combine aspects of a bond and an ETF. ETN returns are based upon the performance of a market index or other reference asset less fees, and can be held to maturity as a debt security. ETNs are traded on a securities exchange. Their value is based on their reference index or strategy and the credit quality of the issuer. ETNs are subject to the additional risk that they may trade at a premium or discount to value attributable to their reference index. When the Fund invests in an ETN, shareholders of the Fund bear their proportionate share of the ETN’s fees and expenses, as well as their share of the Fund’s fees and expenses. There may also not be an active trading market available for some ETNs. Additionally, trading of ETNs may be halted and ETNs may be delisted by the listing exchange.

Fixed Income Securities. Fixed income securities pay interest, dividends or distributions at a specified rate. The rate may be a fixed percentage of the principal or adjusted periodically. In addition, the issuer of a fixed income security must repay the principal amount of the security, normally within a specified time. Fixed income securities provide more regular income than equity securities. However, the returns on fixed income securities are limited and normally do not increase with the issuer’s earnings. This limits the potential appreciation of fixed income securities as compared to equity securities.

A security’s yield measures the annual income earned on a security as a percentage of its price. A security’s yield will increase or decrease depending upon whether it costs less (a discount) or more (a premium) than the principal amount. If the issuer may redeem the security before its scheduled maturity, the price and yield on a discount or premium security may change based upon the probability of an early redemption. Securities with higher risks generally have higher yields.

Interest rate risk is the risk that a fixed income security will lose value because of changes in interest rates. An increase in interest rates may lower a Fund’s value and the overall return on your investment. A wide variety of market factors can cause interest rates to rise, including central bank monetary policy, rising inflation and changes in general economic conditions. Currently, interest rates in the United States are near historic lows. Very low or negative interest rates may magnify interest rate risk for the markets as a whole and for a Fund. Changing interest rates, including rates that fall below zero, may have unpredictable effects on markets, may result in heightened market volatility and may detract from a Fund’s performance. To the extent a Fund has a bank deposit or holds a debt instrument with a negative interest rate to maturity, the Fund would generate a negative return on that investment. Rising interest rates may lead to decreased liquidity in the bond markets, making it more difficult for a Fund to value or sell some or all of its bond holdings at any given time.

Certain instruments in which a Fund may invest rely in some fashion upon the London Interbank Offered Rate (LIBOR). The United Kingdom’s Financial Conduct Authority, which regulates LIBOR, has announced plans to phase out the use of LIBOR by the end of 2021. There remains uncertainty regarding the nature of any replacement for LIBOR, and any potential effects of the transition away from LIBOR on a Fund or on certain instruments in which a Fund invests are not known. The transition process from LIBOR to alternative interest rate benchmarks may not be orderly, may occur over various time periods and may involve, among other things, increased volatility or illiquidity in markets for instruments that currently rely on LIBOR. The transition may also affect the value, liquidity or return on certain Fund investments and may result in costs incurred in connection with closing out positions and entering into new trades, adversely impacting the value of certain instruments held by a Fund or reduce the effectiveness of related Fund transactions such as hedges. Any such effects of the transition away from LIBOR, as well as other unintended consequences and unforeseen effects, could result in losses to the Fund. The impact of any successor or substitute reference rate, if any, will vary on an investment-by-investment basis, and any differences may be material and/or create material economic mismatches. In addition, although certain Fund investments may provide for a successor or substitute reference rate (or terms governing how to determine a successor or substitute reference rate) if the reference rate becomes unavailable, certain Fund investments may not provide such a successor or substitute reference rate (or terms governing how to determine a successor or substitute reference rate). There may be disputes as to: (i) any successor or substitute reference rate; or (ii) the enforceability of any Fund investment that does not provide such a successor or substitute reference rate (or terms governing how to determine a successor or substitute reference rate).

Foreign Securities. Each Fund may invest in foreign securities. The Bond Fund, the Income Fund and the Low Duration Fund may only invest in U.S. dollar denominated foreign securities. The Bond Fund and the Low Duration Fund may invest in securities issued by foreign governments, agencies and corporations. The Income Fund may invest in securities issued by foreign corporations. The Low Duration Fund may invest in foreign money market instruments. Investing in foreign securities involves a series of risks not present in investing in U.S. securities. Most of the foreign securities held by the Funds will not be registered with the SEC, nor will the foreign issuers be subject to SEC reporting requirements. Accordingly, there may be less publicly available information concerning foreign issuers of securities held by the Funds than is available concerning U.S. companies. Disclosure and regulatory standards in many respects are less stringent in emerging market countries than in the U.S. and other major markets. There also may be a lower level of monitoring and regulation of emerging markets and the activities of investors in such markets and enforcement of existing regulations may be extremely limited. Foreign companies and, in particular, companies in smaller and emerging markets are not generally subject to uniform accounting, auditing and financial reporting standards, or to other regulatory requirements comparable to those applicable to U.S. companies.

The costs attributable to foreign investing that a Fund must bear frequently are higher than those attributable to domestic investing; this is particularly true with respect to emerging markets. For example, the costs of maintaining custody of foreign securities exceeds custodian costs for domestic securities and transaction and settlement costs of foreign investing also frequently are higher than those attributable to domestic investing. Costs associated with the exchange of currencies also make foreign investing more expensive than domestic

investing. Investment income and capital gains from certain foreign securities in which a Fund may invest may be subject to foreign withholding or other taxes that could reduce the return of these securities. Tax treaties between the United States and foreign countries, however, may reduce or eliminate the amount of foreign tax to which a Fund would be subject. In addition, a Fund may invest in passive foreign investment companies, which are subject to additional federal income tax considerations, as described further in the “General Trust Information—Federal Income Tax Matters” section.

The economies of individual emerging market and developing countries may differ favorably or unfavorably from the U.S. economy in such respects as growth of gross domestic product, rate of inflation, currency depreciation, capital reinvestment, resource self-sufficiency and balance of payments position. Further, the economies of developing countries generally are heavily dependent upon international trade and, accordingly, have been and may continue to be adversely affected by trade barriers, exchange controls, managed adjustments in relative currency values and other protectionist measures imposed or negotiated by the countries with which they trade. These economies also have been and may continue to be adversely affected by economic conditions in the countries with which they trade.

Investments in companies domiciled in developing countries may be subject to potentially higher risks than investments in developed countries. These risks include: (i) less social, political and economic stability; (ii) the small current size of the markets for such securities and the currently low or nonexistent volume of trading, which result in a lack of liquidity and in greater price volatility; (iii) certain national policies that may restrict a Fund’s investment opportunities, including restrictions on investment in issuers or industries deemed sensitive to national interests; (iv) the absence of developed legal structures governing private or foreign investment or allowing for judicial redress for injury to private property; (v) the absence of a capital market structure or market-oriented economy; and (vi) the possibility that favorable economic developments may be slowed or reversed by unanticipated economic, political or social events in such countries.

In addition, many countries in which the Funds may invest have experienced substantial, and in some periods extremely high, rates of inflation in the past. Inflation and rapid fluctuations in inflation rates have had and may continue to have negative effects on the economies and securities markets of certain countries.

Investments in some foreign countries may involve risks of nationalization, expropriation and confiscatory taxation. The Communist governments of a number of countries expropriated large amounts of private property in the past, in many cases without adequate compensation, and there can be no assurance that such expropriation will not occur in the future. In the event of expropriation, a Fund could lose a substantial portion of any investments it has made in the affected countries. Finally, even though certain currencies may be convertible into U.S. dollars, the conversion rates may be artificial to the actual market values and may be adverse to portfolio shareholders. Further, no accounting standards exist in certain foreign countries.

The Funds endeavor to buy and sell foreign currencies on as favorable a basis as practicable. Some price spread in currency exchange (to cover service charges) will be incurred, particularly when a Fund changes investments from one country to another or when proceeds of the sale of shares in U.S. dollars are used for the purchase of securities in foreign countries. Also, some countries may adopt policies that would prevent a Fund from transferring cash out of the country or withhold portions of interest and dividends at the source. There is the possibility of cessation of trading on national exchanges, withholding and other foreign taxes on income or other amounts, foreign exchange controls (which may include suspension of the ability to transfer currency from a given country), default in foreign government securities, political or social instability, or diplomatic developments that could affect investments in securities of issuers in foreign nations.

Foreign markets also have different clearance and settlement procedures and in certain markets there have been times when settlements have failed to keep pace with the volume of securities transactions, making it difficult to conduct such transactions. The inability of a Fund to make intended security purchases due to settlement problems could cause a Fund to miss investment opportunities. Inability to dispose of a portfolio security due to

settlement problems either could result in losses to a Fund due to subsequent declines in the value of such portfolio security or, if a Fund has entered into a contract to sell the security, could result in possible liability to the purchaser.

The system of share registration and custody in some emerging market countries may create certain risks of loss (including in some cases the risk of total loss) and the Funds may be required to establish special custodial or other arrangements before making investments in these countries. There is an increased risk of uninsured loss due to lost, stolen or counterfeit stock certificates or unauthorized trading, or other fraudulent activity.

On January 31, 2020, the United Kingdom withdrew from the European Union (the “EU”) subject to a withdrawal agreement that permits the United Kingdom to effectively remain in the EU from an economic perspective during a transition phase that expires at the end of 2020. During this transition phase, the United Kingdom and the EU will seek to negotiate and finalize a new, more permanent trade deal. Due to political uncertainty, it is not possible to anticipate whether the United Kingdom and the EU will be able to agree on and implement a new trade agreement or what the nature of such trade arrangement will be. In the event that no agreement is reached, the relationship between the United Kingdom and the EU would be based on the World Trade Organization rules. The extent of the impact of the withdrawal in the United Kingdom and in global markets as well as any associated adverse consequences remain unclear, and the uncertainty may have a significant negative effect on the value of a Fund’s investments. While certain measures are being proposed and/or will be introduced, at the EU level or at the member state level, which are designed to minimize disruption in the financial markets, it is not currently possible to determine whether such measures would achieve their intended effects. The impact of Brexit and the events surrounding the United Kingdom’s withdrawal from the EU may also have an impact on the performance of a Fund’s assets or investments economically tied to the United Kingdom or Europe.

Certain areas of the world historically have been prone to major natural disasters, such as hurricanes, earthquakes, typhoons, flooding, tidal waves, tsunamis, erupting volcanoes, wildfires or droughts, and have been economically sensitive to environmental events. Such disasters, and the resulting damage, could have a severe and negative impact on a Fund’s investment portfolio and, in the longer term, could impair the ability of issuers in which a Fund invests to conduct their businesses in the manner normally conducted. Adverse weather conditions may also have a particularly significant negative affect on issuers in the agricultural sector and on insurance companies that insure against the impact of natural disasters.

Depository Receipts. Foreign securities may be purchased through depository receipts, including American Depository Receipts (“ADRs”), European Depository Receipts (“EDRs”), Global Depository Receipts (“GDRs”) or other securities convertible into securities of foreign issuers. These securities may not necessarily be denominated in the same currency as the securities into which they may be converted. Generally, ADRs, in registered form, are denominated in U.S. dollars and are designed for use in the U.S. securities markets, while EDRs and GDRs may be denominated in other currencies and are designed for use in the European securities markets. ADRs are receipts typically issued by a U.S. bank or trust company evidencing ownership of the underlying securities. EDRs and GDRs are European receipts evidencing a similar arrangement. For purposes of the Funds’ investment policies, ADRs, EDRs and GDRs are deemed to have the same classification as the underlying securities they represent, except that ADRs, EDRs and GDRs shall be treated as indirect foreign investments. Thus, an ADR, EDR or GDR representing ownership of common stock will be treated as common stock. ADR, EDR and GDR depository receipts do not eliminate all of the risks associated with directly investing in the securities of foreign issuers.

ADR facilities may be established as either “unsponsored” or “sponsored.” While ADRs issued under these two types of facilities are in some respects similar, there are distinctions between them relating to the rights and obligations of ADR holders and the practices of market participants.

A depository may establish an unsponsored facility without participation by (or even necessarily the acquiescence of) the issuer of the deposited securities, although typically the depository requests a letter of non-

objection from such issuer prior to the establishment of the facility. Holders of unsponsored ADRs generally bear all the costs of such facilities. The depository usually charges fees upon the deposit and withdrawal of the deposited securities, the conversion of dividends into U.S. dollars, the disposition of non-cash distributions and the performance of other services. The depository of an unsponsored facility frequently is under no obligation to pass through voting rights to ADR holders with respect to the deposited securities. In addition, an unsponsored facility is generally not obligated to distribute communications received from the issuer of the deposited securities or to disclose material information about such issuer in the U.S. and thus there may not be a correlation between such information and the market value of the depository receipts.

Sponsored ADR facilities are created in generally the same manner as unsponsored facilities, except that the issuer of the deposited securities enters into a deposit agreement with the depository. The deposit agreement sets out the rights and responsibilities of the issuer, the depository and the ADR holders. With sponsored facilities, the issuer of the deposited securities generally will bear some of the costs relating to the facility (such as dividend payment fees of the depository), although ADR holders continue to bear certain other costs (such as deposit and withdrawal fees). Under the terms of most sponsored arrangements, depositories agree to distribute notices of shareholder meetings and voting instructions and to provide shareholder communications and other information to the ADR holders at the request of the issuer of the deposited securities.

Risks of Investing in Russia. The United States and European Union have instituted various sanctions against certain Russian officials. These sanctions and other intergovernmental actions that may be undertaken against Russia may result in the devaluation of Russian currency, a downgrade in the country’s credit rating, and a decline in the value and liquidity of Russian stocks. These sanctions could result in the immediate freeze of Russian securities, impairing the ability of a Fund to buy, sell, receive or deliver those securities. In addition, retaliatory action by the Russian government could involve the seizure of assets and any such actions are likely to impair the value and liquidity of such assets. Any or all of these potential results could harm Russia’s economy. These sanctions, and the continued disruption of the Russian economy, could have a negative effect on the performance of a Fund.

Risks of Investing through China Stock Connect. The Shanghai-Hong Kong and Shenzhen-Hong Kong stock connect program (the “Stock Connect”) is a securities trading and clearing links program developed by Hong Kong Exchanges and Clearing Limited (“HKEX”), the Shanghai Stock Exchange (“SSE”), the Shenzhen Stock Exchange (“SZSE”) and China Securities Depositary and Clearing Corporation Limited (“ChinaClear”) with an aim to achieve mutual stock market access between the People’s Republic of China (“PRC”) and Hong Kong.

Quota Limitations. The Stock Connect is subject to quota limitations; in particular, once the remaining balance of the relevant quota drops to zero or the daily quota is exceeded, buy orders will be rejected (although investors will be permitted to sell their cross-boundary securities regardless of the quota balance). Therefore, quota limitations may restrict a Fund’s ability to invest through the Stock Connect on a timely basis, and the relevant Fund may not be able to effectively pursue its investment strategy.

Legal/Beneficial Ownership. The SSE and SZSE A-shares in respect of the Funds are held by the Depositary/sub-custodian in accounts in the Hong Kong Central Clearing and Settlement System maintained by the Hong Kong Securities Clearing Company Limited (“HKSCC”) as central securities depositary in Hong Kong. HKSCC in turn holds the SSE and SZSE A-shares, as the nominee holder, through an omnibus securities account in its name registered with ChinaClear. The precise nature and rights of the Funds as the beneficial owners of the SSE and SZSE A-shares through HKSCC as nominee is not well defined under PRC law. Because HKSCC is only a nominee holder and not the beneficial owner of SSE or SZSE A-shares, in the unlikely event that HKSCC becomes subject to winding up proceedings in Hong Kong, investors should note that SSE and SZSE A-shares will not be regarded as part of the general assets of HKSCC available for distribution to creditors even under Mainland China law. However, HKSCC will not be obliged to take any legal action or enter into court proceedings to enforce any rights on behalf of investors in SSE or SZSE A-shares in Mainland China. Foreign investors, like the Funds investing through the Stock Connect holding the SSE or SZSE A-shares through

HKSCC, are the beneficial owners of the assets and are therefore eligible to exercise their rights through the nominee only.

Clearing and Settlement Risk. HKSCC and ChinaClear have established the clearing links and each has become a participant of the other to facilitate clearing and settlement of cross-boundary trades. For cross-boundary trades initiated in a market, the clearing house of that market will on one hand clear and settle with its own clearing participants, and on the other hand undertake to fulfill the clearing and settlement obligations of its clearing participants with the counterparty clearing house. As the national central counterparty of the PRC’s securities market, ChinaClear operates a comprehensive network of clearing, settlement and stock holding infrastructure. ChinaClear has established a risk management framework and measures that are approved and supervised by the China Securities Regulatory Commission. The chances of ChinaClear default are considered to be remote. In the remote event of a ChinaClear default, HKSCC’s liabilities in SSE and SZSE A-shares under its market contracts with clearing participants will be limited to assisting clearing participants in pursuing their claims against ChinaClear. HKSCC should in good faith, seek recovery of the outstanding stocks and monies from ChinaClear through available legal channels or through ChinaClear’s liquidation. In that event, the relevant Fund may suffer delay in the recovery process or may not fully recover its losses from ChinaClear.

Suspension Risk. Each of the Stock Exchange of Hong Kong (“SEHK”), SSE and SZSE reserves the right to suspend trading if necessary for ensuring an orderly and fair market and that risks are managed prudently. Consent from the relevant regulator would be sought before a suspension is triggered. Where a suspension is effected, a Fund’s ability to access the PRC market will be adversely affected.

Differences in Trading Day. The Stock Connect only operates on days when both the PRC and Hong Kong markets are open for trading and when banks in both markets are open on the corresponding settlement days. It is therefore possible that there are occasions when it is a normal trading day for the PRC market but the Funds cannot carry out any trading via the Stock Connect. The Funds may be subject to a risk of price fluctuations during the time when the Stock Connect is not trading as a result.

Restrictions on Selling Imposed by Front-end Monitoring. PRC regulations require that before an investor sells any A-share, there should be sufficient shares in the account; otherwise the SSE or SZSE will reject the sell order concerned. SEHK will carry out pre-trade checking on sell orders of its participants (i.e., the stock brokers) to ensure there is no over-selling. If a Fund intends to sell certain A-shares it holds, it must transfer those shares to the respective accounts of its broker(s) before the market opens on the day of selling (“trading day”). If it fails to meet this deadline, it will not be able to sell those shares on the trading day. Because of this requirement, a Fund may not be able to dispose of its holdings in a timely manner.

Operational Risk. The Stock Connect is premised on the functioning of the operational systems of the relevant market participants. Market participants are permitted to participate in this program subject to meeting certain information technology capability, risk management and other requirements as may be specified by the relevant exchange and/or clearing house. The securities regimes and legal systems of the two markets differ significantly and market participants may need to address issues arising from the differences on an on-going basis. There is no assurance that the systems of the SEHK and market participants will function properly or will continue to be adapted to changes and developments in both markets. In the event that the relevant systems fail to function properly, trading in both markets through Stock Connect could be disrupted. A Fund’s ability to access the market (and hence to pursue its investment strategy) may be adversely affected.

Regulatory Risk. The Stock Connect is a novel concept. The current regulations are untested and there is no certainty as to how they will be applied. In addition, the current regulations are subject to change and there can be no assurance that the Stock Connect will not be abolished. New regulations may be issued from time to time by the regulators/stock exchanges in the PRC and Hong Kong in connection with operations, legal enforcement and cross-border trades under the Stock Connect. Funds may be adversely affected as a result of such changes.

Recalling of Eligible Stocks. When a stock is recalled from the scope of eligible stocks for trading via the Stock Connect, the stock can only be sold but is restricted from being bought. This may affect the investment portfolio or strategies of the relevant Funds, for example, if the Adviser wishes to purchase a stock that is recalled from the scope of eligible stocks.

No Protection by Investor Compensation Fund. Investment in SSE and SZSE A-shares via the Stock Connect is conducted through brokers, and is subject to the risks of default by such brokers’ in their obligations. Investments of Funds are not covered by the Hong Kong’s Investor Compensation Fund, which has been established to pay compensation to investors of any nationality who suffer pecuniary losses as a result of default of a licensed intermediary or authorized financial institution in relation to exchange-traded products in Hong Kong. Since default matters in respect of SSE and SZSE A-shares via Stock Connect do not involve products listed or traded in SEHK or Hong Kong Futures Exchange Limited, they will not be covered by the Investor Compensation Fund. Therefore, the Funds are exposed to the risks of default of the broker(s) it engages in its trading through the Stock Connect.

Forward Foreign Currency Transactions. The foreign securities held by each Fund, except the Bond Fund, the Income Fund and the Low Duration Fund, will usually be denominated in foreign currencies and the Funds may hold foreign currency in connection with such investments. As a result, the value of the assets held by the Funds may be affected favorably or unfavorably by changes in foreign currency exchange rates, by exchange control regulations and by indigenous economic and political developments. Some countries in which the Funds may invest may also have fixed or managed currencies that are not free-floating against the U.S. dollar. Further, certain currencies may not be internationally traded. Certain of these currencies have historically experienced a steady devaluation relative to the U.S. dollar. Any continued devaluations in the currencies in which a Fund’s securities are denominated may have a detrimental impact on that Fund.

A Fund may enter into forward foreign currency contracts (“forward currency contracts”) in an effort to control some of the uncertainties of foreign currency rate fluctuations. The Funds may engage in forward currency contracts as an attempt to hedge against changes in foreign currency exchange rates affecting the values of securities that the Funds hold or intend to purchase. A forward currency contract is an agreement to purchase or sell a specific currency at a specified future date and price agreed to by the parties at the time of entering into the contract. The Funds will not engage in forward currency contracts in which the specified future date is more than one year from the time of entering into the contract. Each Fund except the Macro Allocation Fund will not enter into a forward currency contract if such contract would obligate the Fund to deliver an amount of foreign currency in excess of the value of the Fund’s securities or other assets denominated in that currency.

The Macro Allocation Fund may also enter into forward currency exchange contracts for purposes of increasing exposure to a foreign currency or to shift exposure to foreign currency fluctuations from one currency to another. To the extent that it does so, the Fund will be subject to the additional risk that the relative value of currencies will be different than anticipated by the Adviser. The use of currency transactions can result in the Fund incurring losses as a result of a number of factors including the imposition of exchange controls, suspension of settlements, or the inability to deliver or receive a specified currency.

The Funds may use forward currency contracts to fix the value of certain securities it has agreed to buy or sell. For example, when a Fund enters into a contract to purchase or sell securities denominated in a particular foreign currency, the Fund could effectively fix the maximum cost of those securities by purchasing or selling a forward currency contract, for a fixed value of another currency, in the amount of foreign currency involved in the underlying transaction. In this way, a Fund can protect the value of securities in the underlying transaction from an adverse change in the exchange rate between the currency of the underlying securities in the transaction and the currency denominated in the forward currency contract during the period between the date the security is purchased or sold and the date on which payment is made or received.

The Funds may also use forward currency contracts to hedge the value, in U.S. dollars, of securities they currently own. For example, if a Fund held securities denominated in a foreign currency and anticipated a

substantial decline (or increase) in the value of that currency against the U.S. dollar, the Fund may enter into a forward currency contract to sell (or purchase), for a fixed amount of U.S. dollars, the amount of foreign currency approximating the value of all or a portion of the securities held which are denominated in such foreign currency.

Upon the maturity of a forward currency transaction, a Fund may either accept or make delivery of the currency specified in the contract or, at any time prior to maturity, enter into a closing transaction that involves the purchase or sale of an offsetting contract. An offsetting contract terminates a Fund’s contractual obligation to deliver the foreign currency pursuant to the terms of the forward currency contract by obligating the Fund to purchase the same amount of the foreign currency, on the same maturity date and with the same currency trader, as specified in the forward currency contract. The Funds realize a gain or loss as a result of entering into such an offsetting contract to the extent the exchange rate between the currencies involved moved between the time of the execution of the original forward currency contract and the offsetting contract.

The use of forward currency contracts to protect the value of securities against the decline in the value of a currency does not eliminate fluctuations in the underlying prices of the securities the Fund owns or intends to acquire, but it does fix a future rate of exchange. Although such contracts minimize the risk of loss resulting from a decline in the value of the hedged currency, they also limit the potential for gain resulting from an increase in the value of the hedged currency. The benefits of forward currency contracts to a Fund will depend on the ability of the Adviser to accurately predict future currency exchange rates.

For forward foreign currency contracts, the Macro Allocation Fund will segregate cash or liquid securities at least in an amount equal to the daily net (marked-to-market) obligation arising from the transaction.

Foreign Currency Futures. Each Fund, except the Bond Fund, the Income Fund and the Low Duration Fund, may enter into foreign currency futures. Generally, foreign futures contracts will be executed on a U.S. exchange. To the extent they are not, however, engaging in such transactions will involve the execution and clearing of trades on or subject to the rules of a foreign board of trade. Neither the National Futures Association nor any domestic (U.S.) exchange regulates the activities of any foreign boards of trade, including the execution, delivery and clearing of transactions, or has the power to compel enforcement of the rules of a foreign board of trade or any applicable foreign law. This is true even if the exchange is formally linked to a domestic market so that a position taken on the exchange may be liquidated by a transaction on the appropriate domestic market. Moreover, applicable laws or regulations will vary depending on the foreign country in which the foreign futures transaction occurs. Therefore, entities (such as the Funds) that trade foreign futures contracts may not be afforded certain of the protective measures provided by the Commodity Exchange Act, CFTC regulations, the rules of the National Futures Association or those of a domestic (U.S.) exchange. In particular, monies received from customers for foreign futures transactions may not be provided the same protections as monies received in connection with transactions on U.S. futures exchanges. In addition, the price of any foreign futures and, therefore, the potential profit and loss thereon, may be affected by any variance in the foreign exchange rate between the time the order for the futures contract is placed and the time it is liquidated, offset or exercised.

High-Yield/High-Risk Securities. Each Fund, except the Income Fund and the Low Duration Fund, may invest in high-yield/high-risk securities. High-yield/high-risk securities (or “junk” bonds) are debt securities rated below investment grade by the primary rating agencies (such as Standard & Poor’s, a division of The McGraw-Hill Companies, Inc., and Moody’s Investors Service, Inc.). The Bond Fund may only invest up to 5% of its net assets in high-yield securities.

High-yield securities usually entail greater risk (including the possibility of default or bankruptcy of the issuers of such securities), generally involve greater volatility of price and risk to principal and income, and may be less liquid, than securities in the higher rating categories. Issuers of such high-yield securities often are highly leveraged and may not have available to them more traditional methods of financing. Therefore, the risk associated with acquiring the securities of such issuers generally is greater than is the case with higher rated

securities. For example, during an economic downturn or a sustained period of rising interest rates, highly leveraged issuers of high-yield securities may experience financial stress. During such periods, such issuers may not have sufficient revenues to meet their interest payment obligations. The issuer’s ability to service its debt obligations may also be adversely affected by specific corporate developments, or the issuer’s inability to meet specific projected business forecasts, or the unavailability of additional financing. The risk of loss from default by the issuer is significantly greater for the holders of high-yield securities because such securities are generally unsecured and are often subordinated to other creditors of the issuer. Prices and yields of high-yield securities will fluctuate over time and, during periods of economic uncertainty, volatility of high-yield securities may adversely affect a Fund’s net asset value.

A Fund may have difficulty disposing of certain high-yield securities because they may have a thin trading market. Because not all dealers maintain markets in all high-yield securities, a Fund anticipates that such securities could be sold only to a limited number of dealers or institutional investors. The lack of a liquid secondary market may have an adverse effect on the market price and a Fund’s ability to dispose of particular issues and may also make it more difficult for a Fund to obtain accurate market quotations for purposes of valuing a Fund’s assets. Market quotations generally are available on many high-yield issues only from a limited number of dealers and may not necessarily represent firm bids of such dealers or prices for actual sales. Adverse publicity and investor perceptions may decrease the values and liquidity of high-yield securities. These securities may also involve special registration responsibilities, liabilities and costs, and liquidity and valuation difficulties. Credit quality in the high-yield securities market can change suddenly and unexpectedly, and even recently-issued credit ratings may not fully reflect the actual risks posed by a particular high-yield security.

Illiquid Securities. Illiquid securities are any investment that the Fund reasonably expects cannot be sold or disposed of in current market conditions in seven calendar days or less without the sale or disposition significantly changing the market value of the investment. The Board of Trustees has adopted a Liquidity Risk Management Program as required by Rule 22e-4 under the 1940 Act, pursuant to which the administrator of the Liquidity Risk Management Program (the “Liquidity Risk Management Program Administrator”) determines and monitors each security’s liquidity. The Board of Trustees has designated the Adviser’s Liquidity Risk Management Committee, which is a multidisciplinary committee comprised of individuals serving in various roles in different departments with the Adviser, as the Liquidity Risk Management Program Administrator.

Investment Companies (each Fund except the Macro Allocation Fund). Subject to the provisions of the 1940 Act (including exemptive relief granted by the Securities and Exchange Commission to other registered investment companies on which the Funds may rely), each Fund, except the Income Fund, may invest in the shares of investment companies that may include exchange-traded funds or business development companies. Investment in other investment companies may provide advantages of diversification and increased liquidity; however, when a Fund invests in another investment company, shareholders of the Fund bear their proportionate share of the other investment company’s fees and expenses as well as their share of the Fund’s fees and expenses. Several foreign governments permit investments by non-residents in their markets only through participation in certain investment companies specifically organized to participate in such markets. In addition, investments in unit trusts and country funds permit diversified investments in foreign markets that are smaller than those in which a Fund would ordinarily invest directly. Investments in such pooled vehicles should enhance the geographical diversification of a Fund’s assets, while reducing the risks associated with investing in certain smaller foreign markets. Investments in such vehicles should provide increased liquidity and lower transaction costs than are normally associated with direct investments in such markets; however, when a Fund invests in another investment company, shareholders of the Fund bear their proportionate share of the other investment company’s fees and expenses as well as their share of the Fund’s fees and expenses.

Investment Companies (Macro Allocation Fund). Subject to the provisions of the 1940 Act (including exemptive relief granted by the SEC to other registered investment companies on which the Fund may rely), the Fund may invest in the shares of investment companies that include exchange-traded funds (“ETFs”). The Fund may also invest in closed-end funds and unit investment trusts. Investment in other investment companies may provide advantages of diversification and increased liquidity; however, when the Fund invests in another investment company, shareholders of the Fund bear their proportionate share of the other investment company’s fees and expenses as well as their share of the Fund’s fees and expenses. Several foreign governments permit investments by non-residents in their markets only through participation in certain investment companies specifically organized to participate in such markets. In addition, investments in unit trusts and country funds permit diversified investments in foreign markets that are smaller than those in which the Fund would ordinarily invest directly. Investments in such pooled vehicles should enhance the geographical diversification of the Fund’s assets, while reducing the risks associated with investing in certain smaller foreign markets. Investments in such vehicles should provide increased liquidity and lower transaction costs than are normally associated with direct investments in such markets; however, when the Fund invests in another investment company, shareholders of the Fund bear their proportionate share of the other investment company’s fees and expenses as well as their share of the Fund’s fees and expenses.

When the Fund invests in ETFs in reliance on exemptive orders granted to the ETFs, the Fund will be subject to any applicable conditions of the exemptive orders or any agreements with the ETFs and may be required to vote such ETFs’ shares in the same proportion as the vote of all other holders of such securities in certain circumstances. The Fund invests in ETFs in reliance on exemptive orders granted to the ETFs.

Investment by the Fund in other investment companies covers a wide variety of asset classes. The risks associated with various types of investment companies that invest in different asset classes are described below. As new investment company products become available, the Fund will be able to invest in those funds, consistent with its investment objective and subject to its investment policies and restrictions.

By investing in securities of other investment companies, the Fund’s shareholders will indirectly bear the fees of that other investment company in addition to the Fund’s own fees and expenses.

Aggressive Investment Technique Risk. Other investment companies may use investment techniques and financial instruments that could be considered aggressive, including the use of futures contracts, options on futures contracts, securities and indices, forward contracts, swap agreements and similar instruments. Another investment company’s investment in financial instruments may involve a small investment relative to the amount of investment exposure assumed and may result in losses exceeding the amounts invested in those instruments. Such instruments, particularly when used to create leverage, may expose the other investment company to potentially dramatic changes (losses or gains) in the value of the instruments and imperfect correlation between the value of the instruments and the relevant security or index. The use of aggressive investment techniques also exposes another investment company to risks different from, or possibly greater than, the risks associated with investing directly in securities on which the aggressive technique is based, including: 1) the risk that an instrument is temporarily mispriced; 2) credit, performance or documentation risk on the amount each other investment company expects to receive from a counterparty; 3) the risk that securities prices, interest rates and currency markets will move adversely and another investment company will incur significant losses; 4) imperfect correlation between the price of financial instruments and movements in the prices of the underlying securities; 5) the risk that the cost of holding a financial instrument might exceed its total return; and 6) the possible absence of a liquid secondary market for any particular instrument and possible exchange imposed price fluctuation limits, both of which may make it difficult or impossible to adjust another investment company’s position in a particular instrument when desired.

Borrowing/Leverage Risk. Other investment companies may borrow money for investment purposes, commonly referred to as “leveraging.” As a result, the other investment company’s exposure to fluctuations in the price of its assets will be increased as compared to its exposure if the fund did not borrow. Borrowing activities by

another investment company will amplify any increase or decrease in the net asset value of the fund. In addition, the interest which the other investment company pays on borrowed money, together with the additional costs of maintaining a borrowing facility, are additional costs borne by the fund and could reduce or eliminate any net investment profits. Unless profits on assets acquired with borrowed funds exceed the costs of borrowing, the use of borrowing will diminish the investment performance of the other investment company compared with what it would have been without borrowing. When the other investment company borrows money it must comply with certain asset coverage requirements, which at times may require the fund to dispose of some of its portfolio holdings even though it may be disadvantageous to do so at the time.

Commodity Risk. Investing in other investment companies that have exposure to investments in the commodities market may subject the Fund to greater volatility than investments in traditional securities. Commodities include metals, energy, agricultural products, livestock and minerals. Certain other investment companies may buy certain commodities (such as gold) or may invest in commodity-linked derivative instruments. The value of commodities and commodity contracts are affected by a variety of factors, including, but not limited to: global supply and demand, changes in interest rates, commodity index volatility, and factors affecting a particular industry or commodity, such as drought, floods, weather, livestock disease, embargos, government regulation, tariffs and taxes, world events and economic, political and regulatory developments. The Fund’s ability to invest in other investment companies that invest in or have exposure to investments in the commodities market may be significantly limited by the federal income tax rules applicable to regulated investment companies.

Concentration Risk. Some other investment companies may be concentrated in a narrow industry. Concentration risk results from maintaining exposure to issuers conducting business in a specific industry. The risk of concentrating investments in a limited number of issuers in a particular industry is that the other investment company will be more susceptible to the risks associated with that industry than a fund that does not concentrate its investments. An index-based other investment company may have significant exposure to individual companies or industry sectors that constitute a significant portion of the referenced index. As a result, such an other investment company will be more susceptible to the risks associated with that specific company or industry sector, which may be different from the risks generally associated with the companies contained in the index. In addition, the Fund may invest in investment companies that focus on hedging or alternative investment strategies.

Correlation Risk. There is a risk that changes in the value of hedging instruments used on other investment companies will not match those of the investment being hedged. Other investment companies benchmarked to an inverse multiple of an index should lose value as the index or security underlying such ETF’s benchmark is increasing (gaining value), a result that is the opposite from traditional mutual funds.

Currency Risk. The Fund’s assets and net asset value are denominated in U.S. dollars. Investing in other investment companies that have exposure to currencies other than the U.S. dollar involves certain risks. The value of such other investment company’s shares relates directly to the value of foreign securities held by the other investment company. Fluctuations in the price of foreign securities could materially and adversely affect the value of the other investment company’s shares. The price of the currency may fluctuate widely. Several factors may affect the price of the currency, including, but not limited to: debt level and trade deficit; inflation rates of the United States and foreign countries and investors’ expectations concerning inflation rates; investment and trading activities of mutual funds, hedge funds and currency funds; and global or regional political, economic or financial events and situations. In addition, a currency may not maintain its long-term value in terms of purchasing power in the future. When the price of the country’s currency declines relative to another currency, it is expected that the price of another investment company’s holding such a currency will decline as well.

Distressed and Defaulted Securities Risk. The other investment companies may invest in the securities of financially distressed and bankrupt issuers, including debt obligations that are in covenant or payment default. Such investments generally trade significantly below par and are considered speculative. The repayment of defaulted obligations is subject to significant uncertainties. Defaulted obligations might be repaid only after lengthy workout or bankruptcy proceedings, during which the issuer might not make any interest or other

payments. Typically such workout or bankruptcy proceedings result in only partial recovery of cash payments or an exchange of the defaulted obligation for other debt or equity securities of the issuer or its affiliates, which may in turn be illiquid or speculative.

Geographical Concentration Risk. Certain other investment companies that focus their investments in particular countries or geographic regions may be particularly susceptible to economic, political or regulatory events affecting those countries or regions. In addition, currency devaluations could occur in countries that have not yet experienced currency devaluation to date, or could continue to occur in countries that have already experienced such devaluations. As a result, other investment companies that focus their investments in a particular geographic region or country may be more volatile than a more geographically diversified fund.

Non-Diversified Risk. Certain other investment companies have the ability to concentrate a relatively high percentage of their investments in the securities of a small number of issuers. This would make the performance of the other investment company more susceptible to a single economic, political or regulatory event than a diversified mutual fund or ETF might be. This risk may be particularly acute with respect to another investment company whose index underlying its benchmark comprises a small number of stocks or other securities.

Limited Liability Companies (“LLCs”). Consistent with its investment objective and policies and subject to the limitations of the Code and the 1940 Act, each Fund may invest in common units or other securities of LLCs, including preferred units, subordinated units and debt securities. LLC common units represent an equity ownership interest in an LLC, entitling the holder to a share of the LLC’s success through distributions and/or capital appreciation. LLCs typically do not pay federal income tax at the entity level and are typically required by their operating agreements to distribute a large percentage of their current operating earnings. In the event of liquidation, LLC common unit holders have a right to the LLC’s remaining assets after bond holders, other debt holders and preferred unit holders, if any, have been paid in full. LLC common units may trade on a national securities exchange or over-the-counter.

Market Conditions and Events. As global economies and financial markets become increasingly interconnected, political, economic and other conditions and events in one country, region, or financial market may adversely impact issuers in a different country, region or financial market. Furthermore, the occurrence of, among other events, natural or man-made disasters, severe weather or geological events, fires, floods, earthquakes, outbreaks of disease (such as COVID-19, avian influenza or H1N1/09), epidemics, pandemics, malicious acts, cyber-attacks, terrorist acts or the occurrence of climate change, may also adversely impact the performance of a Fund. Such events may result in, among other things, closing borders, exchange closures, health screenings, healthcare service delays, quarantines, cancellations, supply chain disruptions, lower consumer demand, market volatility and general uncertainty. Such events could adversely impact issuers, markets and economies over the short- and long-term, including in ways that cannot necessarily be foreseen. A Fund could be negatively impacted if the value of a portfolio holding were harmed by such political or economic conditions or events. In addition, governments, their regulatory agencies, or self-regulatory organizations may take actions in response to such conditions and events that affect the instruments in which the Fund invests, or the issuers of such instruments, in ways that could have a significant negative impact on the Fund’s investment performance. Moreover, such negative political and economic conditions and events could disrupt the processes necessary for a Fund’s operations.

New Companies. The Growth Fund, the Large Cap Growth Fund, the Mid Cap Growth Fund, the Small-Mid Cap Core Fund, the Small-Mid Cap Growth Fund, the Small-Mid Cap Value Fund, the Small Cap Growth Fund, the Small Cap Value Fund, the Global Leaders Fund, the International Leaders Fund, the International Growth Fund, the Institutional International Growth Fund, the International Small Cap Growth Fund, the Emerging Markets Leaders Fund, the Emerging Markets Growth Fund, the Emerging Markets Small Cap Growth Fund and the Macro Allocation Fund may invest their assets in the securities of companies with continuous operations of

less than three years (“new companies”). Investments in new companies involve considerations that are not applicable to investing in securities of established, larger-capitalization issuers, including reduced and less reliable information about issuers and markets, less stringent financial disclosure requirements and accounting standards, illiquidity of securities and markets, higher brokerage commissions and fees and greater market risk in general. In addition, securities of new companies may involve greater risks since these securities may have limited marketability and, thus, may be more volatile. Because such companies normally have fewer shares outstanding than larger companies, it may be more difficult for the Funds to buy or sell significant amounts of such shares without an unfavorable impact on prevailing prices. These companies may have limited product lines, markets or financial resources and may lack management depth. In addition, these companies are typically subject to a greater degree of changes in business prospects than are larger, more established companies. There is typically less publicly available information concerning these companies than for larger, more established ones.

Although investing in securities of these companies offers potential for above-average returns if the companies are successful, the risk exists that the companies will not succeed and the prices of the companies’ shares could significantly decline in value. Therefore, an investment in the Funds may involve a greater degree of risk than an investment in other mutual funds that seek capital appreciation by investing in more established, larger companies.

Publicly Traded Partnerships. Publicly traded partnerships are limited partnerships (or limited liability companies), the units of which are listed and traded on a securities exchange. The Funds may invest in publicly traded partnerships that are treated as partnerships for federal income tax purposes. These include master limited partnerships (“MLPs”) and other entities qualifying under limited exceptions in the Code. Many MLPs derive income and capital gain from the exploration, development, mining or production, processing, refining, transportation or marketing of any mineral or natural resource, or from real property. The value of MLP units fluctuates predominantly based on prevailing market conditions and the success of the MLP. The Funds may purchase common units of an MLP on an exchange as well as directly from the MLP or other parties in private placements. Unlike owners of common stock of a corporation, owners of common units have limited voting rights and have no ability to annually elect directors. MLPs generally distribute all available cash flow (cash flow from operations less maintenance capital expenditures) in the form of quarterly distributions, but a Fund will be required for federal income tax purposes to include in its taxable income its allocable share of the MLP’s income regardless of whether any distributions are made by the MLP. Thus, if the distributions received by a Fund are less than that Fund’s allocable share of the MLP’s income, the Fund may be required to sell other securities so that it may satisfy the requirements to qualify as a regulated investment company and avoid federal income and excise taxes. Common units typically have priority as to minimum quarterly distributions. In the event of liquidation, common units have preference over subordinated units, but not debt or preferred units, to the remaining assets of the MLP.

An investment in MLP units involves some risks that differ from an investment in the common stock of a corporation. Holders of MLP units have limited control and voting rights on matters affecting the partnership. Holders of MLP units of a particular MLP are also exposed to a remote possibility of liability for the obligations of that MLP under limited circumstances not expected to be applicable to the Funds. In addition, the value of a Fund’s investment in MLPs depends largely on the MLPs being treated as partnerships for federal income tax purposes. If an MLP does not meet current federal income tax requirements to maintain partnership status, or if it is unable to do so because of federal income tax law changes, it would be taxed as a corporation. In that case, the MLP would be obligated to pay federal income tax at the entity level and distributions received by a Fund generally would be taxed as dividend income for federal income tax purposes. As a result, there could be a reduction in a Fund’s cash flow and there could be a material decrease in the value of that Fund’s shares. A Fund will not acquire any interests in MLPs that are believed to expose the assets of the Fund to liabilities incurred by the MLP.

invest primarily in real estate that produces income from rentals. “Mortgage” REITs invest primarily in mortgages and derive their income from interest payments. REITs usually specialize in a particular type of property and may concentrate their investments in particular geographical areas. REITs issue stocks and most REIT stocks trade on the major stock exchanges or over-the-counter. REITs are subject to volatility from risks associated with investments in real estate and investments dependent on income from real estate, such as fluctuating demand for real estate and sensitivity to adverse economic conditions. In addition, the failure of a REIT to continue to qualify as a REIT for federal income tax purposes would have an adverse effect upon the value of an investment in that REIT.

Repurchase Agreements. In a repurchase agreement, a Fund buys a security at one price and at the time of sale, the seller agrees to repurchase the security at a mutually agreed upon time and price (usually within seven days). The repurchase agreement thereby determines the yield during the purchaser’s holding period, while the seller’s obligation to repurchase is secured by the value of the underlying security. The Adviser will monitor, on an ongoing basis, the value of the underlying securities to ensure that the value always equals or exceeds the repurchase price plus accrued interest. Repurchase agreements could involve certain risks in the event of a default or insolvency of the other party to the agreement, including possible delays or restrictions upon a Fund’s ability to dispose of the underlying securities. The risk to a Fund is limited to the ability of the seller to pay the agreed upon sum on the delivery date. In the event of default, a repurchase agreement provides that a Fund is entitled to sell the underlying collateral. The loss, if any, to a Fund will be the difference between the proceeds from the sale and the repurchase price. However, if bankruptcy proceedings are commenced with respect to the seller of the security, disposition of the collateral by the Fund may be delayed or limited. Although no definitive creditworthiness criteria are used, the Adviser reviews the creditworthiness of the banks and non-bank dealers with which a Fund enters into repurchase agreements to evaluate those risks. The Adviser will review and monitor the creditworthiness of broker-dealers and banks with which a Fund enters into repurchase agreements. A Fund may, under certain circumstances, deem repurchase agreements collateralized by U.S. Government securities to be investments in U.S. Government securities.

Restricted Securities. Restricted securities may be sold only in privately negotiated transactions or in a public offering with respect to which a registration statement is in effect under the Securities Act of 1933, as amended (the “Securities Act”). Where registration is required, a Fund may be obligated to pay all or part of the registration expenses and a considerable period may elapse between the time of the decision to sell and the time the portfolio may be permitted to sell a security under an effective registration statement. If, during such a period, adverse market conditions were to develop, a Fund might obtain a less favorable price than prevailed when it decided to sell. If through the appreciation of restricted securities or the depreciation of unrestricted securities, a Fund would be in a position where more of its net assets are invested in illiquid securities, including restricted securities that are not readily marketable (except for 144A Securities and 4(a)(2) commercial paper deemed to be liquid), than is permitted by its investment restrictions, the Fund will take such steps as it deems advisable, if any, in accordance with its procedures for monitoring liquidity.

Reverse Repurchase Agreements. The Macro Allocation Fund may enter into reverse repurchase agreements. Reverse repurchase agreements involve the sale of securities held by the Fund pursuant to the Fund’s agreement to repurchase the securities at an agreed upon price, date and rate of interest. During the reverse repurchase agreement period, the Fund continues to receive principal and interest payments on these securities. Such agreements are considered to be borrowings under the 1940 Act. While reverse repurchase transactions are outstanding, the Fund will cover the market value of the securities, plus accrued interest. Reverse repurchase agreements involve the risk that the market value of the securities sold by the Fund may decline below the price at which the Fund is obligated to repurchase such securities.

Royalty Income Trusts. A royalty income trust is a trust whose securities are listed on a securities exchange, generally in Canada or the U.S., and that controls an underlying company whose business is the acquisition, exploitation, production and sale of oil and natural gas. Royalty income trusts generally pay out to unit holders the majority of the cash flow that they receive from the production and sale of underlying oil and natural gas

reserves. The amount of distributions paid on royalty income trust units will vary from time to time based on production levels, commodity prices, royalty rates and certain expenses, deductions and costs, as well as on the distribution payout ratio policies adopted. As a result of distributing the bulk of their cash flow to unit holders, the ability of a royalty income trust to finance internal growth through exploration is limited. Royalty income trusts generally grow through acquisition of additional oil and gas properties or producing companies with proven reserves of oil and gas, funded through the issuance of additional equity or, where the trust is able, additional debt. Royalty income trusts are exposed to many of the same risks as energy and natural resources companies, such as commodity pricing risk, supply and demand risk and depletion and exploration risk.

Section 4(a)(2) Paper. The Low Duration Fund and the Macro Allocation Fund may invest in commercial paper issued in reliance upon the so-called “private placement” exemption from registration afforded by Section 4(a)(2) of the Securities Act of 1933 (“Section 4(a)(2) paper”). The Bond Fund and the Macro Allocation Fund may also invest in Section 4(a)(2) paper from time to time in connection with certain mortgage-backed transactions. Section 4(a)(2) paper is restricted as to disposition under the federal securities laws, and generally is sold to institutional investors such as the Fund. Any resale by the purchaser must be in an exempt transaction. Section 4(a)(2) paper normally is resold to other institutional investors through or with the assistance of the issuer or investment dealers who make a market in the Section 4(a)(2) paper, thus providing liquidity. The Adviser considers the legally restricted but readily saleable Section 4(a)(2) paper to be liquid; however, pursuant to the procedures approved by the Board of Trustees, if a particular investment in Section 4(a)(2) paper is not determined to be liquid, that investment will be included within the limitation on illiquid securities. Information on the procedures for liquidity determinations for the Funds’ portfolio holdings and the ongoing monitoring of Fund liquidity is provided under the heading “Illiquid Securities.”

Short Sales. The Macro Allocation Fund can sell securities short. Selling securities short involves selling securities the seller (e.g., the Fund) does not own (but has borrowed) in anticipation of a decline in the market price of such securities. To deliver the securities to the buyer, the seller must arrange through a broker to borrow the securities and, in so doing, the seller becomes obligated to replace the securities borrowed at their market price at the time of the replacement. In a short sale, the proceeds the seller receives from the sale may be retained by the broker until the seller replaces the borrowed securities. The seller may have to pay a premium to borrow the securities and must pay any dividends or interest payable on the securities until they are replaced.

A short sale is “against the box” if, at all times during which the short position is open, the Fund owns at least an equal amount of the securities or securities convertible into, or exchangeable without further consideration for, securities of the same issuer as the securities that are sold short.

The Fund can also maintain short positions in forward currency exchange transactions, in which the Fund agrees to exchange currency that it does not own at that time for another currency at a future date and specified price in anticipation of a decline in the value of the currency sold short relative to the currency that the Fund has contracted to receive in the exchange. In some cases (e.g., with respect to forwards that are contractually required to “cash-settle”), the Fund will cover the amount of the daily net (marked-to-market) obligation arising from the transaction, rather than the notional amount of the underlying contract. By covering the amount of the net obligation rather than the notional amount, the Fund will have the ability to employ leverage to a greater extent than if it set aside cash or other liquid assets equal to the notional amount of the contract which may increase the risk associated with such transactions.

Short-Term Trading. The Macro Allocation Fund may engage in short-term trading. Securities may be sold in anticipation of a market decline or purchased in anticipation of a market rise and later sold. In addition, a security may be sold and another purchased at approximately the same time to take advantage of what the Fund believes to be a temporary disparity in the normal yield relationship between the two securities. Such trading would be expected to increase the Fund’s portfolio turnover rate and the expenses incurred in connection with such trading and may result in recognition of greater levels of short-term capital gain, which is taxed to shareholders as ordinary income when distributed by the Fund.

Small Companies. While smaller companies generally have the potential for rapid growth, investments in smaller companies often involve greater risks than investments in larger, more established companies because smaller companies may lack the management experience, financial resources, product diversification and competitive strengths of larger companies. In addition, in many instances the securities of smaller companies are traded only over-the-counter or on a regional securities exchange and the frequency and volume of their trading is substantially less than is typical of larger companies. Therefore, the securities of smaller companies may be subject to greater and more abrupt price fluctuations. When making large sales, a Fund may have to sell portfolio holdings at discounts from quoted prices or may have to make a series of small sales over an extended period of time due to the trading volume of smaller company securities. These risks are intensified for investments in micro-cap companies. Investors should be aware that, based on the foregoing factors, an investment in Mid Cap Growth Fund, Small-Mid Cap Growth Fund, the Small-Mid Cap Core Fund, Small-Mid Cap Value Fund, Small Cap Growth Fund, Small Cap Value Fund, Global Leaders Fund, International Small Cap Growth Fund, Emerging Markets Growth Fund, Emerging Markets Small Cap Growth Fund and Macro Allocation Fund and, to a lesser extent, Growth Fund, Large Cap Growth Fund, International Leaders Fund, International Growth Fund, Institutional International Growth Fund and Emerging Markets Leaders Fund may be subject to greater price fluctuations than an investment in a fund that invests primarily in larger, more established companies. The Adviser’s research efforts may also play a greater role in selecting securities for the portfolio than in a fund that invests in larger, more established companies.

Special Purpose Acquisition Companies. The Growth Fund, the Large Cap Growth Fund, the Mid Cap Growth Fund, the Small-Mid Cap Core Fund, the Small-Mid Cap Growth Fund, the Small-Mid Cap Value Fund, the Small Cap Growth Fund, the Small Cap Value Fund, the Global Leaders Fund, the International Leaders Fund, the International Growth Fund, the Institutional International Growth Fund, the International Small Cap Growth Fund, the Emerging Markets Leaders Fund, the Emerging Markets Growth Fund and the Emerging Markets Small Cap Growth Fund may invest in stock, warrants and other securities of special purpose acquisition companies (“SPACs”) or similar special purpose entities that pool funds to seek potential acquisition opportunities. Unless and until an acquisition is completed, a SPAC generally invests its assets (less a portion retained to cover operating expenses) in U.S. Government securities, money market securities and cash; if an acquisition that meets the requirements for the SPAC is not completed within a pre-established period of time, the SPAC dissolves and returns to investors their pro rata share of the assets. Because SPACs and similar entities are in essence blank check companies without an operating history or ongoing business other than seeking acquisitions, the value of their securities is particularly dependent on the ability of the entity’s management to identify and complete a profitable acquisition that will be subject to shareholder approval. Some SPACs may pursue acquisitions only within certain industries or regions, which may increase the volatility of their prices.

Temporary Defensive Position. Each Fund may significantly alter its make-up as a temporary defensive strategy. A defensive strategy will be employed if, in the judgment of the Adviser, investments in a Fund’s usual markets or types of investments become decidedly unattractive because of current or anticipated non-normal market conditions, including adverse economic, financial, political and social factors. For temporary defensive purposes, a Fund may invest up to 100% of its assets in other types of securities or assets, including high-quality commercial paper, obligations of banks and savings institutions, U.S. Government securities, government agency securities and repurchase agreements, or it may retain funds in cash. At such time as the Adviser determines that a Fund’s defensive strategy is no longer warranted, a Fund will adjust its portfolio back to its normal complement of securities as soon as practicable. When a Fund is invested defensively, it may not meet its investment objective.

U.S. Government Securities. There are two broad categories of U.S. Government-related debt instruments: (a) direct obligations of the U.S. Treasury, and (b) securities issued or guaranteed by U.S. Government agencies.

Examples of direct obligations of the U.S. Treasury are Treasury bills, notes, bonds and other debt securities issued by the U.S. Treasury. These instruments are backed by the “full faith and credit” of the United States. They differ primarily in interest rates, the length of maturities and the dates of issuance. Treasury bills have

original maturities of one year or less. Treasury notes have original maturities of one to ten years and Treasury bonds generally have original maturities of greater than ten years.

Some agency securities are backed by the full faith and credit of the United States (such as Maritime Administration Title XI Ship Financing Bonds and Agency for International Development Housing Guarantee Program Bonds) and others are backed only by the rights of the issuer to borrow from the U.S. Treasury, while still others, such as the securities of the Federal Farm Credit Bank, are supported only by the credit of the issuer. With respect to securities supported only by the credit of the issuing agency or by an additional line of credit with the U.S. Treasury, there is no guarantee that the U.S. Government will provide support to such agencies and such securities may involve risk of loss of principal and interest.

U.S. Government securities may include “zero coupon” securities that have been stripped by the U.S. Government of their unmatured interest coupons and collateralized obligations issued or guaranteed by a U.S. Government agency or instrumentality.

Interest rates on U.S. Government obligations may be fixed or variable. Interest rates on variable rate obligations are adjusted at regular intervals, at least annually, according to a formula reflecting then current specified standard rates, such as 91-day U.S. Treasury bill rates. These adjustments generally tend to reduce fluctuations in the market value of the securities.

The government guarantee of the U.S. Government securities in a Fund’s portfolio does not guarantee the net asset value of the shares of a Fund. There are market risks inherent in all investments in securities and the value of an investment in a Fund will fluctuate over time. Normally, the value of investments in U.S. Government securities varies inversely with changes in interest rates. For example, as interest rates rise the value of investments in U.S. Government securities will tend to decline, and as interest rates fall the value of a Fund’s investments will tend to increase. In addition, the potential for appreciation in the event of a decline in interest rates may be limited or negated by increased principal prepayments with respect to certain mortgage-backed securities, such as Ginnie Mae Certificates. Prepayments of high interest rate mortgage-backed securities during times of declining interest rates will tend to lower the return of a Fund and may even result in losses to a Fund if some securities were acquired at a premium. Moreover, during periods of rising interest rates, prepayments of mortgage-backed securities may decline, resulting in the extension of a Fund’s average portfolio maturity. As a result, a Fund’s portfolio may experience greater volatility during periods of rising interest rates than under normal market conditions.

Variable Rate Securities. The Bond Fund, the Income Fund, the Low Duration Fund and the Macro Allocation Fund may invest in instruments having rates of interest that are adjusted periodically or that “float” continuously or periodically according to formulae intended to minimize fluctuation in values of the instruments (“Variable Rate Securities”). The interest rate on a Variable Rate Security is ordinarily determined by reference to, or is a percentage of, an objective standard such as the LIBOR, a bank’s prime rate, the 90-day U.S. Treasury Bill rate or the rate of return on commercial paper or bank certificates of deposit. Generally, the changes in the interest rates on Variable Rate Securities reduce the fluctuation in the market value of such securities. Accordingly, as interest rates decrease or increase, the potential for capital appreciation or depreciation is less than for fixed-rate obligations. The Fund may invest in Variable Rate Securities that have a demand feature entitling the Fund to resell the securities to the issuer or a third party at an amount approximately equal to the principal amount thereof plus accrued interest (“Variable Rate Demand Securities”). As is the case for other Variable Rate Securities, the interest rate on Variable Rate Demand Securities varies according to some objective standard intended to minimize fluctuation in the values of the instruments. Many of these Variable Rate Demand Securities are unrated, their transfer is restricted by the issuer and there is little if any secondary market for the securities. Thus, any inability of the issuers of such securities to pay on demand could adversely affect the liquidity of these securities.

period or perpetually. Warrants may be acquired separately or in connection with the acquisition of securities. Warrants do not carry with them the right to dividends or voting rights with respect to the securities that they entitle their holder to purchase and they do not represent any rights in the assets of the issuer. As a result, warrants may be considered to have more speculative characteristics than certain other types of investments. In addition, the value of a warrant does not necessarily change with the value of the underlying securities and a warrant ceases to have value if it is not exercised prior to its expiration date.

When-Issued or Delayed Delivery Transactions. Each Fund may purchase newly issued securities on a when-issued basis and may purchase or sell portfolio securities on a delayed delivery basis (including on a to-be-announced (TBA) basis). When a Fund purchases securities on a when-issued or a delayed delivery basis, it becomes obligated to purchase the securities and it has all the rights and risks attendant to ownership of the securities, although delivery and payment occur at a later date. A Fund will record the transaction and reflect the liability for the purchase and the value of the security in determining its net asset value. The value of fixed income securities to be delivered in the future will fluctuate as interest rates vary. A Fund generally has the ability to close out a purchase obligation on or before the settlement date, rather than take delivery of the security.

At the time a Fund makes the commitment to sell a security on a delayed delivery basis, it will record the transaction and include the proceeds to be received in determining its net asset value; accordingly, any fluctuations in the value of the security sold pursuant to a delayed delivery commitment are ignored in calculating net asset value so long as the commitment remains in effect. Normally, settlement occurs within one month of the purchase or sale.

To the extent a Fund engages in when-issued or delayed delivery purchases, it will do so for the purpose of acquiring securities consistent with the Fund’s investment objective and policies and not for the purpose of investment leverage or to speculate on interest rate changes. A Fund may also engage in when-issued or delayed delivery purchases for the purpose of managing risk associated with interest rate changes. Each Fund reserves the right to sell securities purchased on a when-issued or delayed delivery basis before the settlement date if deemed advisable.

General. The public offering price of all share classes of a Fund is the next determined net asset value. No initial sales charge or contingent deferred sales charge is imposed. Since a Fund’s shares are sold without an initial sales charge, the full amount of the investor’s purchase payment will be invested in shares for the investor’s account. Orders for the purchase of shares of a Fund will be confirmed at a price based on the net asset value of that Fund next determined after receipt by the Distributor or the transfer agent of the order accompanied by payment. However, orders received by dealers or other financial services firms prior to the determination of net asset value (see “General Trust Information—Determination of Net Asset Value”) and transmitted to the Distributor or the transfer agent prior to a specified time before the start of the next business day will be confirmed at a price based on the net asset value determined on the day the order was received by the dealer or financial services firm (“trade date”). The Funds reserve the right to determine the net asset value more frequently than once a day if deemed desirable. Dealers and other financial services firms are obligated to transmit orders promptly. Collection may take significantly longer for a check drawn on a foreign bank than for a check drawn on a domestic bank. Therefore, if an order is accompanied by a check drawn on a foreign bank, funds must normally be collected before shares will be purchased.

Investment dealers and other firms provide varying arrangements for their clients to purchase and redeem the Funds’ shares. Some may establish a higher minimum investment requirement than established by the Funds. Firms may arrange with their clients for other investment or administrative services. Such firms may independently establish and charge additional amounts to their clients for such services, which charges would

reduce the clients’ return. Firms also may hold the Funds’ shares in nominee or street name as agent for and on behalf of their customers. In such instances, the Funds’ transfer agent will have no information with respect to or control over the accounts of specific shareholders. Such shareholders may obtain access to their accounts and information about their accounts only from their firm. Certain of these firms may receive compensation from the Funds through the Distributor for recordkeeping and other expenses relating to these nominee accounts. In addition, certain privileges with respect to the purchase and redemption of shares or the reinvestment of dividends may not be available through such firms. Some firms may participate in a program allowing them access to their client’s accounts for servicing including, without limitation, transfers of registration and dividend payee changes, and may perform functions such as generation of confirmation statements and reimbursement of cash dividends. Such firms may receive compensation from the Funds through the Distributor for these services. This Statement of Additional Information should be read in connection with such firms’ material regarding their fees and services.

The Funds reserve the right to withdraw all or any part of the offering made by this Statement of Additional Information and reject purchase orders. Also, from time to time, each Fund may temporarily suspend the offering of any class of its shares to new investors. During the period of such suspension, persons who are already shareholders of such class of such Fund may be permitted to continue to purchase additional shares of such class and to have dividends reinvested.

Certain financial intermediaries are authorized to accept purchase and redemption orders for the Funds’ shares. Those financial intermediaries may also designate other parties to accept purchase and redemption orders on the Funds’ behalf. Orders for purchase or redemption will be deemed to have been received by the Trust when such financial intermediaries or their authorized designees accept the orders. Subject to the terms of the contract between the Distributor and the financial intermediary, ordinarily orders will be priced at the Fund’s net asset value next computed after acceptance by such financial intermediaries or their authorized designees. Further, if purchases or redemptions of a Fund’s shares are arranged and settlement is made at an investor’s election through any other financial intermediary, that financial intermediary may, at its discretion, charge a fee for that service. The Trust and the Distributor each has the right to limit the amount of purchases by, and to refuse to sell to, any person. The Trust and the Distributor may suspend or terminate the offering of shares of a Fund at any time for any reason.

Summary of Fees Paid to William Blair for Class N Shares. In addition to a management fee, under the Distribution Plan, the Funds pay a distribution fee to the Distributor, payable monthly, at the annual rate of 0.25% of average daily net assets of each Fund (0.15% of the Bond Fund, the Income Fund and the Low Duration Fund) attributable to Class N shares. The fee is accrued daily as an expense of Class N shares. Class N shares of the Funds may reimburse William Blair for fees paid to intermediaries such as banks, broker-dealers, financial advisers or other financial institutions for sub-administration, sub-transfer agency and other services provided to shareholders whose shares are held of record in omnibus, other group accounts, retirement plans or accounts traded through registered securities clearing agents. See “Other Payments to Third Parties and Affiliates” for more information.

Summary of Fees Paid to William Blair for Class I Shares. In addition to a management fee, Class I shares of the Funds may reimburse William Blair for fees paid to intermediaries such as banks, broker-dealers, financial advisers or other financial institutions for sub-administration, sub-transfer agency and other services provided to shareholders whose shares are held of record in omnibus, other group accounts, retirement plans or accounts traded through registered securities clearing agents. See “Other Payments to Third Parties and Affiliates” for more information. The Funds do not pay a distribution fee for Class I shares.

Summary of Fees Paid to William Blair for Class R6 Shares and Institutional Funds. Class R6 shares of the Funds as well as the Institutional International Growth Fund pay a management fee but do not pay a distribution fee, sub-administration or sub-transfer agency fee.

Share Certificates. Share certificates will not be issued for any share class of the Funds.

Suspension of Redemption or Delay in Payment. The Trust may not suspend the right of redemption or delay payment on its shares for more than seven days except (a) during any period when the New York Stock Exchange is closed (other than on weekends and customary holidays); (b) when trading in the markets that the portfolio normally utilizes is restricted or any emergency exists as determined by the SEC, so that disposal of a Fund’s investments or determination of its net asset value is not reasonably practicable; or (c) for such other periods as the SEC may permit by order for protection of the Trust’s shareholders.

Special Redemptions. Although it is the present policy of the Funds to redeem shares in cash, the Trust reserves the right to pay the redemption price in whole or in part by a distribution of portfolio instruments in lieu of cash, in conformity with the applicable rules of the SEC, taking such instruments at the same value used to determine net asset value and selecting the instruments in such manner as the Board of Trustees may deem fair and equitable. If such a distribution occurs, shareholders receiving instruments and selling them before their maturity could receive less than the redemption value of such instruments and could also incur transaction costs. The Funds have elected to be governed by Rule 18f-1 under the 1940 Act, pursuant to which the Funds are obligated to redeem portfolio shares solely in cash up to the lesser of $250,000 or 1% of the net asset value of the portfolio during any 90-day period for any one shareholder of record. Distributions of portfolio instruments in redemption of shares is a taxable event to the redeeming shareholder for federal income tax purposes.

Exchange Privileges. Shareholders of Class N, Class I and Class R6 shares may exchange their shares for shares of the corresponding class of other William Blair Funds in accordance with the provisions set forth in the applicable Fund’s prospectus.

General. Exchanges will be effected by redeeming your shares and purchasing shares of the other William Blair Fund or William Blair Funds requested. Shares of a William Blair Fund with a value in excess of $1 million acquired by exchange from another William Blair Fund may not be exchanged thereafter until they have been owned for 15 days (the “15 Day Hold Policy”). For purposes of determining whether the 15-Day Hold Policy applies to a particular exchange, the value of the shares to be exchanged shall be computed by aggregating the value of shares being exchanged for all accounts under common control, discretion or advice, including without limitation accounts administered by a financial services firm offering market timing, asset allocation or similar services. The Funds reserve the right to reject any exchange order for any reason, including excessive, short-term (market timing) or other abusive trading practices that may disrupt portfolio management. The total value of shares being exchanged must at least equal the minimum investment requirement of the William Blair Fund into which they are being exchanged. Exchanges are made based on relative dollar values of the shares involved in the exchange. There is no service fee for an exchange; however, dealers or other firms may charge for their services in effecting exchange transactions. For federal income tax purposes, any such exchange constitutes a sale upon which a gain or loss may be realized, depending upon whether the value of the shares being exchanged is more or less than the shareholder’s adjusted cost basis of such shares. Shareholders interested in exercising the exchange privilege may obtain prospectuses of the other William Blair Funds from dealers, other firms or the Distributor. Exchanges may be accomplished by a written request or by telephone if the shareholder has given authorization. During periods when it is difficult to contact the Transfer Agent by telephone, it may be difficult to use the telephone exchange privilege. The exchange privilege is not a right and may be suspended, terminated or modified at any time. Exchanges may only be made for the William Blair Funds that are available for sale in the shareholder’s state of residence.

Conversion Privilege. Class N shareholders who are eligible to invest in Class I shares may request a conversion of their Class N shares to Class I shares of the same Fund. Class I shareholders who are eligible to invest in Class R6 shares may request a conversion of their Class I shares to Class R6 shares of the same Fund. The Funds will consider such requests on a case by case basis, provided eligibility requirements and relevant minimums are met. For federal income tax purposes, a same-Fund conversion is not expected to result in the realization by the investor of a capital gain or loss.

Determination of Net Asset Value. For each Fund, net asset value is determined as of the close of regular trading on the New York Stock Exchange, which is generally 3:00 p.m., Central time (4:00 p.m., Eastern time). Net asset value is not determined on the days that the New York Stock Exchange is closed, which generally includes the observance of New Year’s Day, Dr. Martin Luther King Jr. Day, President’s Day, Good Friday, Memorial Day, Independence Day, Labor Day, Thanksgiving Day and Christmas Day. Net asset value is not required to be computed on a day when no orders to purchase shares were received and no shares were tendered for redemption.

U.S. Equity Securities. The value of U.S. equity securities, including exchange-traded funds, is determined by valuing securities traded on national securities markets or in the over-the-counter markets at the last sale price or, if applicable, the official closing price or, in the absence of a recent sale on the date of determination, at the mean between the last reported bid and ask prices. Investments in other investment funds which are not traded on an exchange are valued at their respective net asset value per share.

Foreign Equity Securities. The value of foreign equity securities is generally determined based upon the last sale price on the foreign exchange or market on which it is primarily traded and in the currency of that market as of the close of the appropriate exchange or, if there have been no sales during that day, at the mean between the last reported bid and ask prices. The Board of Trustees has determined that the passage of time between when the foreign exchanges or markets close and when a Fund computes its net asset value could cause the value of foreign equity securities to no longer be representative or accurate and, as a result, may necessitate that such securities be fair valued. Accordingly, for foreign equity securities, a Fund may use an independent pricing service to fair value price the security as of the close of regular trading on the New York Stock Exchange. As a result, a Fund’s value for a security may be different from the last sale price (or the mean between the last reported bid and ask prices).

Domestic and Foreign Fixed Income Securities. Fixed income securities are generally valued using evaluated prices provided by an independent pricing service. The evaluated prices are formed using various market inputs that the pricing service believes accurately represent the market value of a security at a particular point in time. The pricing service determines evaluated prices for fixed income securities using inputs including, but not limited to, recent transaction prices, dealer quotes, transaction prices for securities with similar characteristics, collateral characteristics, credit quality, payment history, liquidity and market conditions. Repurchase agreements are valued at cost, which approximates fair value.

Derivative Instruments. Option contracts on securities, currencies and other financial instruments traded on one or more exchanges are valued at their most recent sale price on the exchange on which they are traded most extensively. Option contracts on foreign indices are valued at the settlement price. Futures contracts (and options and swaps thereon) are valued at the most recent settlement price on the exchange on which they are traded most extensively. Forward foreign currency contracts are valued on the basis of the value of the underlying currencies at the prevailing currency exchange rate as supplied by an independent pricing service.

Subsidiary. The Macro Allocation Fund’s shares of its Subsidiary are valued at the net asset value per share of the Subsidiary, which is calculated using the same valuation procedures as the Fund.

Other Valuation Factors. Securities, and other assets, for which a market price is not available, is deemed unreliable (e.g., securities affected by unusual or extraordinary events, such as natural disasters or securities affected by market or economic events, such as bankruptcy filings), or the value of which is affected by a significant valuation event, are valued at a fair value as determined in good faith by, or under the direction of, the Board of Trustees and in accordance with the Trust’s valuation procedures. The value of fair valued securities may be different from the last sale price (or the mean between the last reported bid and ask prices), and there is no guarantee that a fair valued security will be sold at the price at which a Fund is carrying the security.

Federal Income Tax Matters. The following is intended to be a general summary of certain federal income tax consequences of investing in one or more Funds. It is not intended as a complete discussion of all such tax consequences, nor does it purport to deal with all categories of investors. This discussion reflects applicable federal income tax laws of the United States as of the date of this Statement of Additional Information, which tax laws may change or be subject to new interpretation by the courts or the Internal Revenue Service (“IRS”), possibly with retroactive effect. Investors are therefore advised to consult with their tax advisors before making an investment in a Fund.

Fund Taxation. Each series (Fund) of the Trust is treated as a separate entity for federal income tax purposes. Each Fund has qualified and elected to be treated as a “regulated investment company” under Subchapter M of the Internal Revenue Code of 1986, as amended (the “Code”), and intends to continue to so qualify in the future. As such, and by complying with the applicable provisions of the Code regarding the sources of its income, the amount and timing of its distributions and the diversification of its assets, each Fund generally will not be subject to federal income tax on its taxable income (including net short-term and net long-term capital gains) that is distributed to shareholders in accordance with the requirements of the Code. However, a Fund would be subject to federal income tax at corporate rates on any undistributed taxable income.

In order to qualify as a regulated investment company, a Fund must, among other things, (i) derive at least 90% of its gross income each taxable year from dividends, interest, payments with respect to certain securities loans, gains from the sale or other disposition of stock, securities or foreign currencies, other income (including but not limited to gains from options, futures or forward contracts) derived with respect to its business of investing in such stock, securities or currencies and net income derived from interests in qualified publicly traded partnerships (“qualifying income”), (ii) distribute with respect to each taxable year an amount equal to or exceeding the sum of 90% of its “investment company taxable income,” as that term is defined in the Code (which generally includes, among other things dividends, interest and the excess of any net short-term capital gains over net long-term capital losses as reduced by certain deductible expenses) without regard to the deduction for dividends paid, and 90% of its tax-exempt interest income, net of expenses allocable thereto and (iii) at the end of each fiscal quarter (a) maintain at least 50% of the value of its total assets in cash and cash items (including receivables), U.S. Government securities, securities of other regulated investment companies and other securities with such other securities limited, with respect to each issuer, to an amount no more than 5% of the value of the Fund’s total assets and 10% of the outstanding voting securities of such issuer and (b) have no more than 25% of the value of its total assets invested in the securities (other than those of the U.S. Government or other regulated investment companies) of any one issuer or of two or more issuers that the Fund controls and that are engaged in the same, similar or related trades or businesses, or the securities of one or more qualified publicly traded partnerships. The requirements for qualification as a regulated investment company may significantly limit the extent to which a Fund may invest in some investments.

Each Fund intends to declare and make distributions during the calendar year of an amount sufficient to prevent imposition of a nondeductible 4% federal excise tax. The required distribution generally is the sum of (1) at least 98% of a Fund’s ordinary income (not taking into account any capital gains or losses) for the calendar year, (2) at least 98.2% of its capital gain net income for the twelve-month period ending on October 31 of such calendar

year and (3) the sum of all undistributed ordinary income and capital gain net income from any prior year, less any over-distribution from any prior year.

If in any taxable year a Fund fails to qualify as a regulated investment company under the Code, such Fund would be taxed in the same manner as an ordinary corporation and distributions to its shareholders would not be deductible by the Fund in computing its taxable income. In such event, a Fund’s distributions (including net tax-exempt interest income and net long-term capital gains, if any), to the extent derived from its current or accumulated earnings and profits, would generally constitute dividends. Such income would generally be eligible for the dividends received deduction available to corporate shareholders. Furthermore, individual and other non-corporate shareholders generally would be able to treat such distributions as “qualified dividend income” eligible for reduced rates of federal income taxation, provided in both cases certain holding period and other requirements are satisfied.

For federal income tax purposes, a Fund is generally permitted to carry forward a net capital loss in any taxable year to offset its own capital gains, if any. These amounts are available to be carried forward to offset future capital gains to the extent permitted by the Code and applicable tax regulations. As of December 31, 2019, the following Funds had capital loss carryforwards approximating the amounts indicated (in thousands):

If a Fund invests in certain positions, such as zero coupon securities, deferred interest securities or, in general, any other securities with original issue discount (or with market discount if the Fund elects to include market discount in income currently), the Fund must accrue income on such investments for each taxable year, which generally will be prior to the receipt of the corresponding cash payments. However, a Fund must distribute, at least annually, all or substantially all of its net investment income, including such accrued income, to shareholders to avoid U.S. federal income and excise taxes. Therefore, a Fund may have to dispose of its portfolio securities under disadvantageous circumstances to generate cash, or may have to leverage itself by borrowing the cash, to satisfy these distribution requirements.

The Funds may acquire market discount bonds. A market discount bond is a security acquired in the secondary market at a price below its redemption value (or its adjusted issue price if it is also an original issue discount bond). If a Fund invests in a market discount bond, it will be required to treat any gain recognized on the disposition of such market discount bond as ordinary income (instead of capital gain) to the extent of the accrued market discount unless the Fund elects to include the market discount in income as it accrues, as discussed above.

A Fund’s investment in lower-rated or unrated debt securities may present issues for the Fund if the issuers of these securities default on their obligations because the federal income tax consequences to a holder of such securities are not certain.

Special federal income tax provisions may accelerate or defer recognition of certain gains or losses, change the character of certain gains or losses or alter the holding periods of certain of a Fund’s securities. Specifically, the mark-to-market rules of the Code may require a Fund to recognize unrealized gains and losses on certain options

on broad-based equity indices, forward contracts, futures and foreign currency futures held by a Fund at the end of its taxable year. Under these provisions, 60% of any gain or loss deemed to be recognized at the end of the Fund’s taxable year or arising from actual sales of such positions during the taxable year will generally be treated as long-term capital gain or loss, and 40% of any such gain or loss will generally be treated as short-term capital gain or loss. Although certain foreign currency forward contracts and foreign currency futures contracts are marked-to-market, any gain or loss related to foreign currency fluctuations is generally treated as ordinary income or loss under Section 988 of the Code (see below). In addition, the straddle rules of the Code require deferral of certain losses realized on positions of a straddle to the extent that the portfolio has unrealized gains in offsetting positions at year end. Furthermore, a Fund’s entry into a short sale transaction, an option or certain other contracts could be treated as the constructive sale of an appreciated financial position, causing such Fund to realize gain, but not loss, on the position.

Generally, the character of the income or capital gains that a Fund receives from another investment company, including certain ETFs, will pass through to the Fund’s shareholders as long as the Fund and the other investment company each qualify as regulated investment companies. However, to the extent that another investment company that qualifies as a regulated investment company realizes net losses on its investments for a given taxable year, a Fund will not be able to recognize its share of those losses until it disposes of shares of such investment company. Moreover, even when a Fund does make such a disposition, a portion of its loss may be recognized as a long-term capital loss. As a result of the foregoing rules, and certain other special rules, it is possible that the amounts of net investment income and net capital gains that a Fund will be required to distribute to shareholders will be greater than such amounts would have been had the Fund invested directly in the securities held by the investment companies in which it invests, rather than investing in shares of the investment companies. For similar reasons, the character of distributions from a Fund (e.g., long-term capital gain, qualified dividend income, etc.) will not necessarily be the same as it would have been had the Fund invested directly in the securities held by the investment companies in which it invests.

Each Fund may invest to a limited degree in publicly traded partnerships that are treated as partnerships for federal income tax purposes. Net income derived from an interest in a qualified publicly traded partnership, which generally includes MLPs, is treated as qualifying income from which a Fund must derive 90% of its gross income. However, at the end of each quarter of its taxable year, no more than 25% of the value of a Fund’s total assets may be invested in securities of qualified publicly traded partnerships. Income a Fund derives from an entity taxed as a partnership but not a qualified publicly traded partnership is treated as qualifying income only to the extent such income is attributable to items of income of the partnership which would be qualifying income if realized directly by the Fund. For federal income tax purposes, a Fund will be taxable on its allocable share of the income of an entity taxed as a partnership regardless of whether the Fund receives any distribution from the partnership. Thus, a Fund may be required to sell other securities in order to satisfy the distribution requirements imposed upon regulated investment companies and to avoid federal income and excise taxes. Distributions from a partnership to a Fund will constitute a return of capital to the extent of the Fund’s basis in the partnership. If a Fund’s basis is reduced to zero, distributions will constitute capital gains for federal income tax purposes.

For taxable years beginning after December 31, 2017 and before January 1, 2026, certain income from investments in MLPs is included in the “combined qualified business income amount” that is eligible for a 20% federal income tax deduction in the case of individuals, trusts and estates. Regulated investment companies currently cannot pass the special character of this income through to shareholders. As a result, direct investors in MLPs may be entitled to this deduction while investors that invest in a Fund that invest in MLPs will not.

Each Fund may invest to a limited degree in royalty income trusts. Distributions from such trusts will be treated as dividend income eligible under the 90% income test described above if the trust is treated as a corporation for U.S. federal income tax purposes. The Funds intend to invest only in royalty income trusts treated as corporations for U.S. federal income tax purposes.

Foreign exchange gains and losses realized by a Fund in connection with certain transactions that involve certain foreign currency-denominated securities, certain foreign currency options, foreign currency forward contracts,

foreign currencies or payables or receivables denominated in a foreign currency are generally subject to Section 988 of the Code, which generally causes such gains and losses to be treated as ordinary income and losses and may affect the amount, timing and character of distributions to shareholders. For example, if a Fund sold a foreign bond and part of the gain or loss on the sale was attributable to an increase or decrease in the value of a foreign currency, then the currency gain or loss may be treated as ordinary income or loss. If such transactions result in higher net ordinary income, the dividends paid by the Fund will be increased.

If a Fund receives an “excess distribution” with respect to stock in a passive foreign investment company (“PFIC”), the Fund itself may be subject to federal income tax on a portion of the excess distribution, whether or not the corresponding income is distributed by the Fund to shareholders. A foreign corporation is classified as a PFIC for a taxable year if at least 50% of its assets constitute investment-type assets or 75% or more of its gross income is investment-type income. In general, under the PFIC rules, an excess distribution is treated as having been realized ratably over the period during which the Fund held the PFIC stock. A Fund itself will be subject to U.S. federal income tax (including interest) on the portion, if any, of an excess distribution that is so allocated to prior taxable years. Certain distributions from a PFIC as well as gain from the sale of PFIC stock are treated as excess distributions. Excess distributions are characterized as ordinary income even though, absent application of the PFIC rules, certain excess distributions might have been classified as capital gain.

A Fund may be eligible to elect alternative tax treatment with respect to PFIC stock. Under a qualified electing fund election that currently is available in certain circumstances, a Fund generally would be required to include in its gross income its share of the PFIC’s income and net capital gain annually, regardless of whether distributions are received from the PFIC in a given year. If this election were made, the special rules discussed above relating to the taxation of excess distributions would not apply. In addition, another election may be available that would involve marking to market a Fund’s PFIC shares at the end of each taxable year (and on certain other dates prescribed in the Code), with the result that unrealized gains are treated as though they were realized and treated as ordinary income or loss (subject to certain limitations). If this election were made, federal income tax at the Fund level under the PFIC rules would generally be eliminated, but the Fund could, in limited circumstances, incur nondeductible interest charges. The Funds have elected, or intend to elect, to mark-to-market their investments, if any, in PFICs. A Fund’s intention to qualify annually as a regulated investment company may limit its options with respect to PFIC shares.

Because the application of the PFIC rules may affect, among other things, the character of gains and the amount of gain or loss and the timing of the recognition of income with respect to PFIC shares, and may subject a Fund itself to tax on certain income from PFIC shares, the amount that must be distributed to shareholders and that will be taxed to shareholders as ordinary income or long-term capital gain may be increased or decreased as compared to a fund that did not invest in PFIC shares.

With respect to the Macro Allocation Fund, the Subsidiary may be classified as a PFIC. However, the CFC rules discussed below will generally supersede the PFIC rules.

A Fund’s investments in REIT equity securities may result in the Fund’s receipt of cash in excess of the REIT’s earnings; if a Fund distributes these amounts, these distributions could constitute a return of capital to Fund shareholders for federal income tax purposes. Investments in REIT equity securities also may require a Fund to accrue and distribute income not yet received. To generate sufficient cash to make the requisite distributions, the Fund may be required to sell securities in its portfolio (including when it is not advantageous to do so) that it otherwise would have continued to hold. Dividends received by a Fund from a REIT will not qualify for the corporate dividends received deduction and generally will not constitute qualified dividend income, although such dividends may be eligible for a 20% deduction with respect to individuals, trusts and estates, as described in more detail below.

Under a notice issued by the IRS, a portion of a Fund’s income from residual interests in real estate mortgage investment conduits (“REMICs”) or from a REIT (or other pass-through entity) that is attributable to the REIT’s

residual interest in a REMIC or an equity interest in a taxable mortgage pool (referred to in the Code as an “excess inclusion”) will be subject to federal income tax in all events. This notice also provides that excess inclusion income of a regulated investment company, such as the Funds, will be allocated to shareholders of the regulated investment company in proportion to the dividends received by such shareholders, with the same consequences as if the shareholders held the related REMIC or taxable mortgage pool interest directly. In general, excess inclusion income allocated to shareholders (i) cannot be offset by net operating losses (subject to a limited exception for certain thrift institutions), (ii) will constitute unrelated business taxable income (“UBTI”) to entities (including a qualified pension plan, an individual retirement account, a 401(k) plan, a Keogh plan or other tax-exempt entity) subject to tax on UBTI, thereby potentially requiring such an entity that is allocated excess inclusion income, and otherwise might not be required to file a federal income tax return, to file a tax return and pay tax on such income, and (iii) in the case of a non-U.S. shareholder, will not qualify for any reduction in U.S. federal withholding tax. In addition, if at any time during any taxable year a “disqualified organization” (as defined by the Code) is a record holder of a share in a regulated investment company, then the regulated investment company will be subject to a tax equal to that portion of its excess inclusion income for the taxable year that is allocable to the disqualified organization, multiplied by the highest federal income tax rate imposed on corporations.

Special Tax Considerations for Macro Allocation Fund. With respect to Macro Allocation Fund, gains from direct investments in commodities and income from certain commodity-linked derivative instruments do not constitute qualifying income. The federal income tax treatment of commodity-linked notes and certain other derivative instruments in which the Fund may invest is not certain, in particular with respect to whether income and gains from such instruments constitutes qualifying income. If the Fund treats income from a particular instrument as qualifying income and the income is later determined not to constitute qualifying income, and, together with any other non-qualifying income, causes the Fund’s non-qualifying income to exceed 10% of its gross income in any taxable year, the Fund will fail to qualify as a regulated investment company unless it is eligible to and does pay a tax at the Fund level. To the extent the Fund seeks to invest in commodities, the Fund may gain exposure to the commodity market by investing a portion of its assets in the Subsidiary. The IRS has issued regulations that generally treat the Fund’s income inclusion with respect to the Subsidiary as qualifying income if there is a distribution in the same taxable year out of the earnings and profits of the Subsidiary that is attributable to such income inclusion, or if the Fund’s income inclusion with respect to the Subsidiary is derived in connection with the Fund’s business of investing in stocks, securities, or currencies.

A foreign corporation, such as the Subsidiary, will generally not be subject to U.S. federal income taxation unless it is deemed to be engaged in a U.S. trade or business. It is expected that the Subsidiary will conduct its activities in a manner so as to meet the requirements of a safe harbor under Section 864(b) (2) of the Code under which the Subsidiary may engage in trading in stocks or securities or certain commodities without being deemed to be engaged in a U.S. trade or business. However, if the Subsidiary’s activities were determined not to be of the type described in the safe harbor, then the activities of the Subsidiary may constitute a U.S. trade or business, and be subject to U.S. federal income tax.

In general, a foreign corporation, such as the Subsidiary, that does not conduct a U.S. trade or business is nonetheless subject to tax at a flat rate of 30% (or lower tax treaty rate), generally payable through withholding, on the gross amount of certain U.S.-source income that is not effectively connected with a U.S. trade or business, subject to certain exemptions, including among others, exemptions for capital gains, portfolio interest and income from notional principal contracts. There is presently no tax treaty in force between the U.S. and the Cayman Islands that would reduce this rate of withholding tax. It is not expected that a material amount of the Subsidiary’s income will be subject to such withholding tax. In addition, the Subsidiary intends to properly certify its status as a non-U.S. person to each custodian and withholding agent to avoid the U.S. backup withholding requirements discussed below.

For federal income tax purposes, the Subsidiary will be treated as a controlled foreign corporation (“CFC”) and the Fund will be treated as a “U.S. shareholder” of the Subsidiary. As a result, the Fund will be required to

include in gross income for U.S. federal income tax purposes all of its Subsidiary’s “subpart F income,” whether or not such income is distributed by the Subsidiary. It is expected that all or substantially all of the Subsidiary’s income will be “subpart F income.” The Fund’s recognition of its Subsidiary’s “subpart F income” will increase the Fund’s basis in its shares of the Subsidiary. Distributions by the Subsidiary to the Fund will be tax-free, to the extent of its previously undistributed “subpart F income,” and will correspondingly reduce the Fund’s basis in its shares of the Subsidiary. “Subpart F income” is generally treated as ordinary income, regardless of the character of the Subsidiary’s underlying income. Therefore, the Fund’s investment in its Subsidiary may cause the Fund to realize more ordinary income than would be the case if the Fund invested directly in the investments held by its Subsidiary. If a net loss is realized by the Subsidiary, such loss is not generally available to offset other income earned by the Fund, and such loss cannot be carried forward to offset taxable income of the Fund or the Subsidiary in future periods.

Shareholder Taxation. Shareholders will be subject to federal income taxes on distributions made by the Funds out of earnings and profits whether received in cash or additional shares of the Funds. Distributions of net investment income (including any net short-term capital gain in excess of any net long-term capital loss), other than qualified dividend income, if any, will be taxable to shareholders as ordinary income. Distributions of qualified dividend income, as such term is defined in Section 1(h)(11) of the Code (generally dividends received from U.S. domestic corporations and qualified foreign corporations), by a Fund to its non-corporate shareholders generally will be taxed at the federal income tax rates applicable to net capital gain, provided certain holding period and other requirements described below are satisfied at both the Fund and shareholder levels. Distributions of net capital gain (the excess of net long-term capital gains over net short-term capital losses), if any, will be taxable to non-corporate shareholders at a maximum federal income tax rate of 20%, without regard to how long a shareholder has held shares of a Fund. Distributions of net investment income received by corporate shareholders of the Fund may qualify for the 50% dividends received deduction generally available to corporations to the extent of the amount of qualifying dividends received by the Fund from domestic corporations during the year, provided that certain holding period and other requirements under the Code are satisfied at both the Fund and shareholder levels. Generally, however, dividends received on stocks of foreign issuers are not eligible for the dividends received deduction.

To be eligible for treatment as qualified dividend income, shareholders generally must hold their shares for more than 60 days during the 121-day period beginning 60 days before the ex-dividend date. In order for dividends received by a Fund’s shareholders to be treated as qualified dividend income, the Fund must also meet holding period and other requirements with respect to such dividend paying stocks it owns. A dividend will not be treated as qualified dividend income at the Fund level if the dividend is received with respect to any share of stock held for 60 days or fewer during the 121-day period beginning on the date that is 60 days before the date on which such share becomes ex-dividend with respect to such dividend (or, in the case of certain preferred stock, 90 days or fewer during the 181-day period beginning 90 days before such date). In addition to the above holding period requirements, a dividend will not be treated as qualified dividend income (at either the Fund or shareholder level), (1) to the extent that the recipient is under an obligation (whether pursuant to a short sale or otherwise) to make related payments with respect to positions in substantially similar or related property, (2) if the recipient elects to have the dividend income treated as investment income for purposes of the limitation on deductibility of investment interest or (3) if the dividend is received from a foreign corporation that is (a) not eligible for the benefits of a comprehensive income tax treaty with the United States (with an exception for stock that is readily tradable on an established securities market in the United States) or (b) treated as a PFIC for its current or preceding taxable year or a surrogate foreign corporation that is not treated as a domestic corporation under Section 7874(b) of the Code.

For taxable years beginning after December 31, 2017 and before January 1, 2026, qualified REIT dividends (i.e., REIT dividends other than capital gain dividends and portions of REIT dividends designated as qualified dividend income) are eligible for a 20% federal income tax deduction in the case of individuals, trusts and estates. A Fund that receives qualified REIT dividends may elect to pass the special character of this income through to its shareholders. To be eligible to treat distributions from a Fund as qualified REIT dividends, a

shareholder must hold shares of the Fund for more than 45 days during the 91-day period beginning on the date that is 45 days before the date on which the shares become ex-dividend with respect to such dividend and the shareholder must not be under an obligation (whether pursuant to a short sale or otherwise) to make related payments with respect to positions in substantially similar or related property. If a Fund does not elect to pass the special character of this income through to shareholders or if a shareholder does not satisfy the above holding period requirements, the shareholder will not be entitled to the 20% deduction for the shareholder’s share of the Fund’s qualified REIT dividend income while direct investors in REITs may be entitled to the deduction.

Distributions declared by a Fund during October, November or December to shareholders of record during such months and paid by January 31 of the following year will be treated for federal income tax purposes as paid by the Fund and received by shareholders on December 31 of the year in which they are declared, rather than in the calendar year in which they are received. After the close of each calendar year, each Fund will notify its shareholders of the amount and type of dividends and distributions it paid.

Gain or loss realized upon a redemption or other disposition (such as an exchange) of shares of a Fund by a shareholder will generally be treated as long-term capital gain or loss if the shares have been held for more than one year and, if not held for such a period, as short-term capital gain or loss. Any loss on the sale or exchange of shares held for six months or less will be treated as a long-term capital loss to the extent of any net capital gain dividends paid to the shareholder with respect to such shares. Any loss a shareholder realizes on a sale or exchange of shares will be disallowed if the shareholder acquires other shares of the Fund (whether through the automatic reinvestment of dividends or otherwise) or substantially identical stock or securities within a 61-day period beginning 30 days before and ending 30 days after the shareholder’s sale or exchange of the shares. In such case, the shareholder’s basis in the shares acquired will be adjusted to reflect the disallowed loss. Capital losses may be subject to limitations on their use by a shareholder.

An additional 3.8% Medicare tax is imposed on certain net investment income (including ordinary dividends and capital gain distributions received from a Fund and net gains from redemptions or other taxable dispositions of Fund shares) of U.S. individuals, estates and trusts to the extent that such person’s “modified adjusted gross income” (in the case of an individual) or “adjusted gross income” (in the case of an estate or trust) exceeds a threshold amount.

When a shareholder opens an account, IRS regulations require that the shareholder provide a taxpayer identification number (TIN), certify that it is correct, and certify that he, she or it is not subject to backup withholding under IRS regulations. If a shareholder fails to provide a TIN or the proper tax certifications, each Fund is required to withhold 24% of all the distributions (including dividends and capital gain distributions) and redemption proceeds paid to the shareholder. Each Fund is also required to begin backup withholding on an account if the IRS instructs it to do so. Amounts withheld may be applied to the shareholder’s federal income tax liability and the shareholder may obtain a refund from the IRS if withholding results in an overpayment of federal income tax for such year.

Foreign Taxation. Investment income received or capital gains recognized by a Fund from sources within foreign countries may be subject to withholding and other taxes imposed by such countries. Tax conventions between certain countries and the U.S. may reduce or eliminate such taxes.

The Funds may qualify for and make an election permitted under the “pass through” provisions of Section 853 of the Code, which allows a regulated investment company to elect to have its foreign tax credit taken by its shareholders. To be eligible for this credit, more than 50% of the value of the Fund’s total assets at the close of its taxable year must consist of stock or securities in foreign corporations, and the Fund must have distributed at least 90% of its (i) investment company taxable income (determined without regard to the deduction for dividends paid) and (ii) net tax-exempt interest income, if any, for such taxable year.

If a Fund makes this election, it may not take any foreign tax credit and may not take a deduction for foreign taxes paid. However, the Fund would be allowed to include the amount of foreign taxes paid in its dividends paid

deduction. Each shareholder would include in his, her or its gross income, and treat as paid by such shareholder, his, her or its proportionate share of the foreign taxes paid by the Fund and may take either a credit or deduction for such foreign taxes on his, her or its federal income tax return, subject in each case to certain limitations contained in the Code. No deduction may be claimed by a shareholder who does not itemize deductions for federal income tax purposes.

If a Fund is not eligible for the election to pass through to its shareholders their proportionate shares of any foreign taxes paid by the Fund, shareholders generally will not be entitled to claim a credit or deduction with respect to foreign taxes incurred by the Fund and will not be required to include such taxes in their gross income.

If the U.S. Government were to impose any restrictions, through taxation or other means, on foreign investments by U.S. investors the Board of Trustees will promptly review the Funds’ policies to determine whether significant changes in its investments are appropriate.

Other Taxes. Dividends and distributions also may be subject to state and local taxes. Shareholders are urged to consult their tax advisors regarding the application of federal, foreign, state and local taxes to their particular situation. Non-U.S. investors who invest in the Funds when such investment is not treated as being effectively connected with the conduct of a U.S. trade or business will generally be subject to U.S. federal income tax treatment that is different from that described above and in the Prospectus. Such investors may be subject to nonresident alien withholding tax at the rate of 30% (or a lower rate under an applicable tax treaty) on dividends and certain other payments from the Funds, and must provide the Funds with an effective IRS Form W-8 or authorized substitute for Form W-8. However, the Fund will generally not be required to withhold tax on any amounts paid to a non-U.S. investor with respect to dividends attributable to “qualified short-term gain” (i.e., the excess of net short-term capital gain over net long-term capital loss) reported as such by the Fund and dividends attributable to certain U.S. source interest income that would not be subject to federal withholding tax if earned directly by a non-U.S. person, provided such amounts are properly reported by the Fund. A Fund may choose not to designate such amounts. Non-U.S. investors should consult their tax advisors regarding such treatment and the application of foreign taxes to an investment in the Funds.

Sections 1471-1474 of the Code and the U.S. Treasury and IRS guidance issued thereunder (collectively, the “Foreign Account Tax Compliance Act” or “FATCA”) generally require a Fund to obtain information sufficient to identify the status of each of its shareholders. If a shareholder fails to provide this information or otherwise fails to comply with FATCA, a Fund may be required to withhold under FATCA at a rate of 30% with respect to that shareholder on Fund dividends. A Fund may disclose the information that it receives from (or concerning) its shareholders to the IRS, non-U.S. taxing authorities or other parties as necessary to comply with FATCA, related intergovernmental agreements or other applicable law or regulation. Each investor is urged to consult its tax advisor regarding the applicability of FATCA and any other reporting requirements with respect to the investor’s own situation, including investments through an intermediary.

Special rules apply to foreign persons who receive distributions from a Fund that are attributable to gain from “United States real property interests” (“USRPIs”). The Code defines USRPIs to include direct holdings of U.S. real property and any interest (other than an interest solely as a creditor) in a “United States real property holding corporation” or former United States real property holding corporation. The Code defines a United States real property holding corporation as any corporation whose USRPIs make up 50% or more of the fair market value of its USRPIs, its interests in real property located outside the United States, plus any other assets it uses in a trade or business. In general, if a Fund is a United States real property holding corporation (determined without regard to certain exceptions), distributions by the Fund that are attributable to (a) gains realized on the disposition of USRPIs by the Fund and (b) distributions received by the Fund from a lower-tier regulated investment company or REIT that the Fund is required to treat as USRPI gain in its hands will retain their character as gains realized from USRPIs in the hands of the Fund’s foreign shareholders and will be subject to U.S. federal withholding tax. In addition, such distributions could result in the foreign shareholder being required to file a U.S. tax return and pay tax on the distributions at regular U.S. federal income tax rates. The consequences to a non-U.S. shareholder,

including the rate of such withholding and character of such distributions (e.g., ordinary income or USRPI gain) will vary depending on the extent of the non-U.S. shareholder’s current and past ownership of a Fund.

In addition, if a Fund is a United States real property holding corporation or former United States real property holding corporation, the Fund may be required to withhold U.S. tax upon a redemption of shares by a greater-than-5% shareholder that is a foreign person, and that shareholder would be required to file a U.S. income tax return for the year of the disposition of the USRPI and pay any additional tax due on the gain. However, no such withholding is generally required with respect to amounts paid in redemption of shares of a fund if the fund is a domestically controlled qualified investment entity, or, in certain other limited cases, if a fund (whether or not domestically controlled) holds substantial investments in regulated investment companies that are domestically controlled qualified investment entities.

Shareholders should consult their tax advisors about the application of the provisions of tax law, including foreign, state and local tax laws, in light of their particular tax situations before investing in the Funds.

Independent Registered Public Accounting Firm. The Trust’s independent registered public accounting firm is Ernst & Young LLP, 155 North Wacker Drive, Chicago, Illinois 60606. Ernst & Young LLP audits and reports upon the Trust’s annual financial statements, reviews certain regulatory reports, reviews the Trust’s federal and state tax returns and performs other professional accounting, auditing, tax and advisory services when engaged to do so by the Trust.

Custodian. The Trust’s custodian, State Street Bank and Trust Company (“State Street”), State Street Financial Center, One Lincoln Street, Boston, Massachusetts 02111, has custody of all securities and cash of the Trust and attends to the collection of principal and income and payment for and collection of proceeds of securities bought and sold by the Trust, as well as certain bookkeeping, data processing and administrative services pertaining to the Trust’s operations, including compliance monitoring and preparation of the Trust’s tax returns. The Adviser pays State Street’s compliance monitoring fees.

Transfer Agent Services. DST Asset Manager Solutions, Inc. (“DST”), 2000 Crown Colony Drive, Quincy, Massachusetts 02169-0953, is the Trust’s transfer agent and dividend-paying agent. DST, as the shareholder service agent, provides certain bookkeeping, data processing and administrative services pertaining to the maintenance of shareholder accounts.

Reports to Shareholders. Shareholders will receive annual audited financial statements and semi-annual unaudited financial statements.

The Funds are the twenty series currently offered for sale by the Trust. All shares of each William Blair Fund have equal rights with respect to dividends, assets and liquidation of a portfolio and equal, noncumulative voting rights. Noncumulative voting rights allow the holder or holders of a majority of shares, voting together for the election of trustees, to elect all the trustees. All shares of each William Blair Fund will be voted in the aggregate, except when a separate vote by a Fund is required under the 1940 Act. Shares are fully paid and nonassessable when issued, are transferable without restriction and have no preemptive or conversion rights.

Under Delaware law, the Trust generally is not required to hold annual shareholders’ meetings. Upon the written request of ten or more shareholders that have held Trust shares for at least six months in an amount equal to the lesser of 1% of the outstanding shares, the Trust will either disseminate appropriate materials (at the expense of the requesting shareholders) or provide such shareholders access to a list of names and addresses of all shareholders of record. The written notice must state that the shareholders making such request wish to communicate with the other shareholders to obtain the signatures necessary to demand a meeting to consider

removal of a trustee. The Trust will hold shareholders’ meetings when requested to do so in writing by one or more shareholders collectively holding at least 10% of the shares entitled to vote, such request specifying the purpose or purposes for which each meeting is to be called, or when determined by a majority of the Board of Trustees in their discretion. Shareholders’ meetings also will be held in connection with the following matters: (1) the election or removal of trustees, if a meeting is called for such purpose; (2) the adoption of any contract for which shareholder approval is required by the 1940 Act; (3) any termination of the Trust, if a meeting is called for such purpose; (4) certain amendments to the Declaration of Trust; (5) any merger, consolidation or sale of all or substantially all assets of the Trust; (6) incorporation of the Trust; and (7) such additional matters as may be required by law, the Declaration of Trust, the By-Laws of the Trust or any registration of the Trust with the SEC or any state, or that the trustees may consider necessary or desirable, such as changes in fundamental investment objectives, policies or restrictions.

The trustees serve until the next meeting of shareholders, if any, called for the purpose of electing trustees and until the election and qualification of their successors or until a director sooner dies, resigns, retires or is removed by a majority vote of the shares entitled to vote or by a majority of the trustees. In accordance with the 1940 Act, the Trust will hold a shareholders’ meeting for the election of trustees at such time that (1) less than a majority of the trustees has been elected by the shareholders and (2) if, as a result of a vacancy in the Board of Trustees, less than two-thirds of the trustees have been elected by the shareholders. A trustee may be removed from office by a vote of the holders of a majority of the outstanding shares entitled to vote.

Derivative Claims of Shareholders. The By-Laws contain provisions regarding derivative claims of shareholders. Under these provisions, a shareholder must make a pre-suit demand upon the Board to bring the subject action unless an effort to cause the Board to bring such an action is not likely to succeed. For purposes of the foregoing sentence, a demand on the Board shall only be deemed not likely to succeed and therefore excused if a majority of the Board, or a majority of any committee of the Board established to consider the merits of such action, is composed of Trustees who are not “independent trustees” (as that term is defined in the Delaware Statutory Trust Act).

Unless a demand is not required under the foregoing first paragraph, shareholders eligible to bring such derivative action under the Delaware Statutory Trust Act who collectively hold at least 10% of the outstanding shares of the Trust, or who collectively hold at least 10% of the outstanding shares of the fund or class to which such action relates, shall join in the request for the Board to commence such action. Further, unless a demand is not required under the foregoing first paragraph, the Board must be afforded a reasonable amount of time to consider such shareholder request and to investigate the basis of such claim. The Board shall be entitled to retain counsel or other advisors in considering the merits of the request and shall require an undertaking by the shareholders making such request to reimburse the Trust for the expense of any such advisors in the event that the Board determine not to bring such action.

Forum for Adjudication of Disputes. The By-Laws provide that, unless the Trust consents in writing to the selection of an alternative forum, the sole and exclusive forum for (i) any derivative action or proceeding brought on behalf of the Trust, (ii) any action asserting a claim of breach of a fiduciary duty owed by any Trustee, officer or other agent of the Trust to the Trust or the Trust’s shareholders, (iii) any action asserting a claim arising pursuant to any provision of the Delaware Statutory Trust Act or the Declaration of Trust or the By-Laws, (iv) any action to interpret, apply, enforce or determine the validity of the Declaration of Trust or the By-Laws or (v) any action asserting a claim governed by the internal affairs doctrine shall be the U.S. District Court for the District of Delaware or the Court of Chancery of the State of Delaware, or, if the Court of Chancery of the State of Delaware does not have jurisdiction, the Superior Court of the State of Delaware.

The By-Laws provide that any person purchasing or otherwise acquiring or holding any interest in shares of beneficial interest of the Trust shall be deemed to have notice of and consented to the provisions relating to forum for adjudication of disputes terms contained in the By-Laws, and to have waived any argument relating to the inconvenience of the forums referenced above in connection with any action or proceeding described in the foregoing paragraph.

This forum selection provision may limit a shareholder’s ability to bring a claim in a judicial forum that it finds favorable for disputes with Trustees, officers or other agents of the Trust and its service providers, which may discourage such lawsuits with respect to such claims. If a court were to find the forum selection provision contained in the By-Laws to be inapplicable or unenforceable in an action, the Trust may incur additional costs associated with resolving such action in other jurisdictions.

The Trust is a Delaware statutory trust organized under a Declaration of Trust dated September 3, 1999. The Trust was formerly organized as a Maryland corporation on September 22, 1987 under the name of William Blair Ready Reserves, Inc. (the “Company”). On April 30, 1991, a reorganization of the Company and Growth Industry Shares, Inc., a Maryland corporation, occurred such that Growth Industry Shares, Inc. was reorganized into a separate portfolio of the Company, the Growth Fund, and the Company changed its name to William Blair Mutual Funds, Inc. On December 15, 1999, the Company was reorganized into the Trust and changed its name to William Blair Funds. The Trust operates as an open-end, management investment company, as defined in the 1940 Act. Presently, the Trust is offering shares of twenty William Blair Funds. All of the series of the Trust are diversified portfolios. The Board of Trustees of the Trust may, however, establish additional portfolios with different investment objectives, policies and restrictions in the future.

The Funds’ audited financial statements, including the notes thereto, contained in the Funds’ annual report to shareholders for the fiscal year ended December 31, 2019, and report of independent registered public accounting firm, are incorporated herein by reference. Additional copies of the annual report to shareholders may be obtained without charge by calling the Trust.

A S&P Global Ratings commercial paper rating is a current assessment of the likelihood of timely payment of debt having an original maturity of no more than 365 days. The following summarizes the rating categories used by S&P Global Standard and Poor’s for commercial paper:

“A-1” - A short-term obligation rated ‘A-1’ is rated in the highest category by S&P Global Ratings. The obligor’s capacity to meet its financial commitments on the obligation is strong. Within this category, certain obligations are designated with a plus sign (+). This indicates that the obligor’s capacity to meet its financial commitments on these obligations is extremely strong.

“A-2” - A short-term obligation rated ‘A-2’ is somewhat more susceptible to the adverse effects of changes in circumstances and economic conditions than obligations in higher rating categories. However, the obligor’s capacity to meet its financial commitments on the obligation is satisfactory.

“A-3” - A short-term obligation rated ‘A-3’ exhibits adequate protection parameters. However, adverse economic conditions or changing circumstances are more likely to weaken an obligor’s capacity to meet its financial commitments on the obligation.

“B” - A short-term obligation rated ‘B’ is regarded as vulnerable and has significant speculative characteristics. The obligor currently has the capacity to meet its financial commitments; however, it faces major ongoing uncertainties that could lead to the obligor’s inadequate capacity to meet its financial commitments.

“C” - A short-term obligation rated ‘C’ is currently vulnerable to nonpayment and is dependent upon favorable business, financial, and economic conditions for the obligor to meet its financial commitments on the obligation.

“D” - A short-term obligation rated ‘D’ is in default or in breach of an imputed promise. For non-hybrid capital instruments, the ‘D’ rating category is used when payments on an obligation are not made on the date due, unless S&P Global Ratings believes that such payments will be made within any stated grace period. However, any stated grace period longer than five business days will be treated as five business days. The ‘D’ rating also will be used upon the filing of a bankruptcy petition or the taking of a similar action and where default on an obligation is a virtual certainty, for example due to automatic stay provisions. A rating on an obligation is lowered to ‘D’ if it is subject to a distressed exchange offer.

Moody’s commercial paper ratings are opinions of the ability of issuers to repay punctually promissory obligations not having an original maturity in excess of one year, unless explicitly noted. The following summarizes the rating categories used by Moody’s for commercial paper:

“P-1” - Issuers (or supporting institutions) rated Prime-1 have a superior ability to repay short-term debt obligations.

“P-2” - Issuers (or supporting institutions) rated Prime-2 have a strong ability to repay short-term debt obligations.

“P-3” - Issuers (or supporting institutions) rated Prime-3 have an acceptable ability to repay short-term obligations.

“NP” - Issuers (or supporting institutions) rated Not Prime do not fall within any of the Prime rating categories.

Fitch Ratings’ short-term ratings apply generally to debt obligations that are payable on demand or have original maturities of up to three years. The following summarizes the rating categories used by Fitch for short-term obligations:

“F-1” - Highest Short-Term Credit Quality. Indicates the strongest intrinsic capacity for timely payment of financial commitments; may have an added “+” to denote any exceptionally strong credit feature.

“F-2” - Good Short-Term Credit Quality. Good intrinsic capacity for timely payment of financial commitments.

“F-3” - Fair Short-Term Credit Quality. The intrinsic capacity for timely payment of financial commitments is adequate.

“B” - Speculative Short-Term Credit Quality. Minimal capacity for timely payment of financial commitments, plus heightened vulnerability to near term adverse changes in financial and economic conditions.

“RD” - Restricted Default. Indicates an entity that has defaulted on one or more of its financial commitments, although it continues to meet other financial obligations. Typically applicable to entity ratings only.

“D” - Default. Indicates a broad-based default event for an entity, or the default of a short-term obligation.

The following summarizes the ratings used by S&P Global Ratings for corporate and municipal debt:

“AAA” - An obligation rated ‘AAA’ has the highest rating assigned by S&P Global Ratings. The obligor’s capacity to meet its financial commitments on the obligation is extremely strong.

“AA” - An obligation rated ‘AA’ differs from the highest-rated obligations only to a small degree. The obligor’s capacity to meet its financial commitments on the obligation is very strong.

“A” - An obligation rated ‘A’ is somewhat more susceptible to the adverse effects of changes in circumstances and economic conditions than obligations in higher-rated categories. However, the obligor’s capacity to meet its financial commitments on the obligation is still strong.

“BBB” - An obligation rated ‘BBB’ exhibits adequate protection parameters. However, adverse economic conditions or changing circumstances are more likely to weaken the obligor’s capacity to meet its financial commitments on the obligation.

“BB,” “B,” “CCC,” “CC,” and “C” - Obligations rated ‘BB’, ‘B’, ‘CCC’, ‘CC’, and ‘C’ are regarded as having significant speculative characteristics. ‘BB’ indicates the least degree of speculation and ‘C’ the highest. While such obligations will likely have some quality and protective characteristics, these may be outweighed by large uncertainties or major exposure to adverse conditions.

“BB” - An obligation rated ‘BB’ is less vulnerable to nonpayment than other speculative issues. However, it faces major ongoing uncertainties or exposure to adverse business, financial, or economic conditions that could lead to the obligor’s inadequate capacity to meet its financial commitments on the obligation.

“B” - An obligation rated ‘B’ is more vulnerable to nonpayment than obligations rated ‘BB’, but the obligor currently has the capacity to meet its financial commitments on the obligation. Adverse business, financial, or economic conditions will likely impair the obligor’s capacity or willingness to meet its financial commitments on the obligation.

“CCC” - An obligation rated ‘CCC’ is currently vulnerable to nonpayment and is dependent upon favorable business, financial, and economic conditions for the obligor to meet its financial commitments on the obligation. In the event of adverse business, financial, or economic conditions, the obligor is not likely to have the capacity to meet its financial commitments on the obligation.

“CC” - An obligation rated ‘CC’ is currently highly vulnerable to nonpayment. The ‘CC’ rating is used when a default has not yet occurred but S&P Global Ratings expects default to be a virtual certainty, regardless of the anticipated time to default.

“C” - An obligation rated ‘C’ is currently highly vulnerable to nonpayment, and the obligation is expected to have lower relative seniority or lower ultimate recovery compared with obligations that are rated higher.

“D” - An obligation rated ‘D’ is in default or in breach of an imputed promise. For non-hybrid capital instruments, the ‘D’ rating category is used when payments on an obligation are not made on the date due, unless S&P Global Ratings believes that such payments will be made within five business days in the absence of a stated grace period or within the earlier of the stated grace period or 30 calendar days. The ‘D’ rating also will be used upon the filing of a bankruptcy petition or the taking of similar action and where default on an obligation is a virtual certainty, for example due to automatic stay provisions. A rating on an obligation is lowered to ‘D’ if it is subject to a distressed exchange offer.

PLUS (+) OR MINUS (-) - Ratings from “AA” to “CCC” may be modified by the addition of a plus (+) or minus (-) sign to show relative standing within the rating categories.

The following summarizes the ratings used by Moody’s for corporate and municipal long-term debt:

“Aaa” - Obligations rated “Aaa” are judged to be of the highest quality, subject to the lowest level of credit risk

“Aa” - Obligations rated “Aa” are judged to be of high quality and are subject to very low credit risk.

“A” - Obligations rated “A” are judged to be upper-medium grade and are subject to low credit risk.

“Baa” - Obligations rated “Baa” are judged to be medium-grade and subject to moderate credit risk and as such may possess certain speculative characteristics.

“Ba” - Obligations rated “Ba” are judged to be speculative and are subject to substantial credit risk.

“B” - Obligations rated “B” are considered speculative and are subject to high credit risk.

“Caa” - Obligations rated “Caa” are judged to be speculative of poor standing and are subject to very high credit risk.

“Ca” - Obligations rated “Ca” are highly speculative and are likely in, or very near, default, with some prospect of recovery of principal and interest.

“C” - Obligations rated “C” are the lowest rated and are typically in default, with little prospect for recovery of principal or interest.

Note: Moody’s appends numerical modifiers 1, 2, and 3 to each generic rating classification from Aa through Caa. The modifier 1 indicates that the obligation ranks in the higher end of its generic rating category; the modifier 2 indicates a mid-range ranking; and the modifier 3 indicates a ranking in the lower end of that generic rating category. Additionally, a “(hyb)” indicator is appended to all ratings of hybrid securities issued by banks, insurers, finance companies, and securities firms.

“AAA” - Highest Credit Quality. “AAA” ratings denote the lowest expectation of credit risk. They are assigned only in cases of exceptionally strong capacity for payment of financial commitments. The capacity is highly unlikely to be adversely affected by foreseeable events.

“AA” - Very High Credit Quality. “AA” ratings denote expectations of very low credit risk. They indicate very strong capacity for payment of financial commitments. This capacity is not significantly vulnerable to foreseeable events.

“A” - High Credit Quality. “A” ratings denote expectations of low credit risk. The capacity for payment of financial commitments is considered strong. This capacity may, nevertheless, be more vulnerable to adverse business or economic conditions than is the case for higher ratings.

“BBB” - Good Credit Quality. “BBB” ratings indicate that expectations of credit risk are currently low. The capacity for payment of financial commitments is considered adequate, but adverse business or economic conditions are more likely to impair this capacity.

“BB” - Speculative. “BB” ratings indicate an elevated vulnerability to credit risk, particularly in the event of adverse changes in business or economic conditions over time; however, business or financial alternatives may be available to allow financial commitments to be met.

“B” - Highly Speculative. “B” ratings indicate that material credit risk is present, but a limited margin of safety remains. Financial commitments are currently being met; however, capacity for continued payment is vulnerable to deterioration in the business and economic environment.

“CCC” - Substantial Credit Risk. “CCC” ratings indicate that default is a real possibility.

“CC” - Very High Levels of Credit Risk. “CC” ratings indicate that default of some kind appears probable.

“C” - Exceptionally High Levels of Credit Risk. “C” indicates that default is imminent or inevitable.

Ratings in the categories of “CCC,” “CC” and “C” can also relate to obligations or issuers that are in default. In this case, the rating does not opine on default risk but reflects the recovery expectation only.

“RD” - Restricted default. “RD” ratings indicate an issuer that in Fitch Ratings’ opinion has experienced an uncured payment default on a bond, loan or other material financial obligation but which has not entered into bankruptcy filings, administration, receivership, liquidation or other formal winding-up procedure, and which has not otherwise ceased operating.

“D” - Default. “D” ratings indicate an issuer that in Fitch Ratings’ opinion has entered into bankruptcy filings, administration, receivership, liquidation or other formal winding-up procedure, or which has otherwise ceased business.

The modifiers “+” or “-” may be appended to a rating to denote relative status within major rating categories.

(x)Amendment to Administration Agreement dated November 1, 2012 (Incorporated herein by reference to Post-Effective Amendment No. 102 to Registrant's Registration Statement on Form N-1A as filed on February 28, 2013).

(xi)Amendment to Administration Agreement dated August 1, 2016 (Incorporated herein by reference to Post-Effective Amendment No. 122 to the Registrant's Registration Statement on Form N-1A as filed on April 28, 2017).

(xii)Form of Amendment to Administration Agreement dated August 1, 2019 (filed herewith).

(i)Opinion and Consent of Dechert LLP (filed herewith).

(j)Consent of Ernst & Young LLP (filed herewith).

(k)Not applicable.

(l)Not applicable.

(m)(i) Amended Distribution Plan – Class N (Incorporated herein by reference to Post-Effective Amendment No. 66 to Registrant's Registration Statement on Form N-1A as Filed on November 30, 2009).

(ii)Distribution Agreement – Class N (Incorporated herein by reference to Post-Effective Amendment No. 71 to Registrant's Registration Statement on Form N-1A as filed on April 29, 2011).

(n)Amended and Restated Multi-Class Plan (Incorporated herein by reference to Post-Effective Amendment No. 128 to Registrant's Registration Statement on Form N-1A as filed on April 30, 2019).

(o)Powers of Attorney for each Trustee, dated February 21, 2019 (Incorporated herein by reference to Post- Effective Amendment No. 126 to Registrant's Registration Statement on Form N-1A as filed on February 27, 2019).

(p)Amended Code of Ethics (Incorporated herein by reference to Post-Effective Amendment No. 120 to the

Registrant's Registration Statement on Form N-1A as filed on April 29, 2016).

ITEM 29. Persons Controlled by or Under Common Control with Registrant

Not applicable.

ITEM 30. Indemnification

Section 5.2 of Article V of the Registrant's Declaration of Trust provides for indemnification of directors and officers under certain circumstances but does not allow such indemnification in cases of willful misfeasance, bad faith, gross negligence, or reckless disregard of the duties involved in the conduct of his office.

Each of the trustees who is not an "interested person" (as defined under the Investment Company Act of 1940) of Registrant (a "Non-interested Trustee") has entered into an indemnification agreement with Registrant, which agreement provides that the Registrant shall indemnify the Non-interested Trustee against certain liabilities which such Trustee may incur while acting in the capacity as a trustee, officer or employee of the Registrant to the fullest extent permitted by law, now or in the future, and requires indemnification and advancement of expenses unless prohibited by law. The indemnification agreement cannot be altered without the consent of the Non-interested Trustee and is not affected by amendment of the Declaration of Trust. In addition, the indemnification agreement adopts certain presumptions and procedures which may make the process of indemnification and advancement of expenses more timely, efficient and certain. In accordance with Section 17(h) of the Investment Company Act of 1940, the indemnification agreement does not protect a Non-interested Trustee against any liability to the Registrant or its shareholders to which such Trustee would otherwise be subject by reason of willful misfeasance, bad faith, gross negligence, or reckless disregard of the duties involved in the conduct of his or her office.

The Registrant has purchased insurance policies insuring its officers and trustees against certain liabilities which such officers and trustees may incur while acting in such capacities and providing reimbursement to the Registrant for sums which it may be permitted or required to pay to its officers and trustees by way of indemnification against such liabilities, subject to certain deductibles.

The Management Agreement between the Registrant and William Blair Investment Management, LLC (the "Adviser") provides that, in the absence of willful misfeasance, bad faith, gross negligence or reckless disregard of obligations or duties thereunder on the part of the Adviser, the Adviser shall not be liable for any error of judgment or mistake of law, or for any loss suffered by the Fund in connection with the matters to which such Agreement relates.

ITEM 31. Business and Other Connections of Investment Adviser

Registrant's investment adviser is William Blair Investment Management, LLC, a limited liability company.

The principal occupations of the partners and primary officers of William Blair Investment Management, LLC are their services as partners and officers of William Blair Investment Management, LLC and/or William Blair & Company, L.L.C., the Registrant's principal underwriter and a dually registered investment adviser and broker- dealer. The address of William Blair Investment Management, LLC, William Blair & Company, L.L.C. and the Registrant is 150 North Riverside Plaza, Chicago, Illinois 60606.

Set forth below is information as to any other business, profession, vocation or employment of a substantial nature in which each partner of William Blair Investment Management, LLC and/or William Blair & Company, L.L.C. is, or at any time during the last two fiscal years has been, engaged for his own account or in the capacity of director, officer, employee, partner or trustee:

Name and Position with
William Blair Investment
Management, LLC
and/or William	Name of Company and/or
Blair &Company, L.L.C.	Principal Business	Capacity

Robert Abbe,

Partner

David L. Adams,

Partner

Jason N. Ader,

Partner

Ryan D. Airola,

Partner

Michael Amez,

Partner

Alaina M. Anderson,

Partner

Jon R. Andersen,

Partner

Andrew Arno,

Partner

Simon Baertl,

Partner

Michael P. Balkin,	William Blair Funds	Senior Vice President
Partner
		8

	Name and Position with
	William Blair Investment
	Management, LLC
	and/or William		Name of Company and/or
	Blair &Company, L.L.C.		Principal Business		Capacity
James Bennett,
Partner
William W. Benton,
Partner
Derek Beres,
Partner
James M. Bertram,
Partner
Ro Bhandari,
Partner
Olga Bitel,
Partner
Edward McC. Blair, Jr.,		Pharos Innovations LLC		Director Life
Partner		Pernix Group, Inc.		Director
Marina S. Bozilenko,		Olema Pharmaceuticals, Inc.		Director
Partner		Arctic Aurora Life Sciences		Director
Stephanie G. Braming,		William Blair Funds		Chairman of the Board and
Partner				President
Christina Bresani,		Bedford Historical Society		Board Member
Partner		Bedford Hills Live		Board Member
David J. Brown,		4FMM, LLC		Investor and Member
Partner
Fritz Buerger,
Partner
Harvey H. Bundy, III,
Partner
Jeffrey A. Burtelow,
Partner
Mike Cavanaugh,
Partner
Manuel Chavez,
Partner
Carl Chiou,
Partner
Ellen-Blair Chube,		Oil-Dri Corporation of America		Board Member
Partner
John Cimaroli,
Partner
Thomas M. Clarke,		William Blair Funds		Senior Vice President
Partner
		9

	Name and Position with
	William Blair Investment
	Management, LLC
	and/or William		Name of Company and/or
	Blair &Company, L.L.C.		Principal Business		Capacity
Daniel J. Connolly,
Partner
James J. Connors,
Partner
E. David Coolidge, III,		Duluth Holdings Inc.		Director
Vice Chairman		Shields Meneley Partners		Advisory Director
		Coolhart Enterprises, LLC		Managing Member
Daniel Crowe,		William Blair Funds		Senior Vice President
Partner
John W. Cultra,
Partner
Kevin Cunningham,
Partner
Benjamin W. Curtis,
Partner
Peter Dalrymple,
Partner
Ryan S. Daniels
Partner
Daniel G. Daul,
Partner
Ryan J. DeVore,		Naval War College Foundation		Trustee
Partner		Merit School of Music		Trustee
		Artisan Gym Floors		Owner
Ryan Dimas,
Partner
Brandon B. Dobell,		Benevolent Enabler, Inc.		Director
Partner		Quicket Solutions, Inc.		Director
		4FMM, LLC		Managing Member
Brian Doherty,
Partner
Gareth A. Down,
Partner
Brian J. Doyle,
Partner
Brian P. Drab,
Partner
Ed Dunphy,
Partner
		10

	Name and Position with
	William Blair Investment
	Management, LLC
	and/or William		Name of Company and/or
	Blair &Company, L.L.C.		Principal Business		Capacity
Robert A. Durkin,
Partner
Robert Duwa,			William Blair Funds		Senior Vice President
Partner
Stephen E. Elkins,
Partner
William G. Escamilla,
Partner
John R. Ettelson,
President and Chief
Executive Officer
Elliot G. Farkas,
Partner
Andrew Feichter,
Partner
Brent W. Felitto,
Partner
Dirk P. Felsmann,
Partner
Simon Fennell,		William Blair Funds		Senior Vice President
Partner
Kevin Fetzer,
Partner
Walid M. Fikri,
Partner
Adam S. Filkin,
Partner
F. Conrad Fischer,		APM Limited Partnership		General Partner
Partner		Chicago Child Care Society		Trustee, Emeritus
Robert C. Fix,		Parker Gale Capital LP		Limited Partner
Partner
Andrew G. Flynn,		William Blair Funds		Senior Vice President
Partner
David C. Fording,		William Blair Funds		Senior Vice President
Partner
Christoph B. Fuchs,
Partner
Sean Gardner,
Partner

	Name and Position with
	William Blair Investment
	Management, LLC
	and/or William		Name of Company and/or
	Blair &Company, L.L.C.		Principal Business		Capacity
Michael Gebo,
Partner
Larry Gilbert,
Partner
Brent W. Gledhill,
Partner
Tyler Glover,		Ronald McDonald House of		Treasurer
Partner		Chicagoland and Northwest Indiana
James S. Golan,		Key Ambassador Co.		Director
Partner		William Blair Funds		Senior Vice President
Richard D. Gottfred,
Partner
Daniel R. Grant,
Partner
Raphael Grunschlag,
Partner
Jim A. Hamman,
Partner
Kyle G. Harris,
Partner
Liam P. Healy,		Killarney Brewing & Distilling Co.		Director
Partner
Andrew M. Hendrie,
Partner
Paul M. Hindsley,		Oil Dri Corporation of America		Director
Partner
Jonathan F. Ho,
Partner
Anthony T. Hoban,
Partner
Christian D. Hodneland,		SAMDI Tech, Inc.		Board of Directors
Partner
Sean Huss,
Partner
Ross Jannotta,
Partner
Steven R. Jesanis,
Partner
Andrew M. Jessen,
Partner
		12

	Name and Position with
	William Blair Investment
	Management, LLC
	and/or William		Name of Company and/or
	Blair &Company, L.L.C.		Principal Business		Capacity
James Jones,		William Blair Funds		Senior Vice President
Partner
Margaret Kaczor,
Partner
James P. Karlis,
Partner
William O. Kasten,		Netsak Storage, LLC		Principal
Partner
Chad M. Kilmer,		William Blair Funds		Senior Vice President
Partner
Adam Klauber,
Partner
Yan Krasov,
Partner
John C. Kreger III,
Partner
Douglas Kryscio,
Partner
Chris Lane,
Partner
Louise Lane,
Partner
Mark R. Lane,
Partner
Robert C. Lanphier, IV,		William Blair Funds		Senior Vice President
Partner
Mark T. Leslie,		William Blair Funds		Senior Vice President
Partner
Stewart Licudi,
Partner
Steve Livingston,
Partner
Brandon W. Lower,
Partner
Timothy F. Lugo,
Partner
Steven E. Maletzky,
Partner
Brian T. Marshall,		Paluch Family Foundation		Board of Directors
Partner
		13

	Name and Position with
	William Blair Investment
	Management, LLC
	and/or William		Name of Company and/or
	Blair &Company, L.L.C.		Principal Business		Capacity
Kelly J. Martin,
Partner
G. Dewey Martinelli,
Partner
Thomas S. Marx,
Partner
Scott A. Mattson,
Partner
Kenneth J. McAtamney,		William Blair Funds		Senior Vice President
Partner

Todd M. McClone, Partner

Robert F. McGuire, Jr.,

Partner

Timothy McHugh, Partner

Cam McKinney,

Partner

Carlette C. McMullan, Partner

Sarah P. Mercurio,

Partner

Samuel A. Miller, Partner

Corey A. Minturn, Partner

David S. Mitchell, Partner

Philipp C. Mohr,

Partner

John C. Moore

Partner

John C. Murphy,

Partner

Erin Murray Butler,

Partner

Robert P. Napoli,

Partner

William Blair Funds

Senior Vice President

William Blair Funds	Senior Vice President
Knox College	Investment Committee Member
Diskus Werke AG	Chairman of the Supervisory Board

William Blair Funds

Senior Vice President

Mission Engine, LLC

Investor and Advisor

	Name and Position with
	William Blair Investment
	Management, LLC
	and/or William		Name of Company and/or
	Blair &Company, L.L.C.		Principal Business		Capacity
DJ Neiman,
Partner
Joseph Niemiec,		Morgenthaler Private Equity		Limited Partner
Partner
Terrence J. O'Bryan,
Partner
James P. O'Connor,		Keeper Security, Inc.		Director
Partner
John F. O'Toole,
Partner
Thomas W. Pace,
Partner
Karl A. Palasz,
Partner
Brett L. Paschke,
Partner
David Port,		Atom Optoelectronics, LLC		Advisory Board
Partner
Casey K. Preyss,		William Blair Funds		Senior Vice President
Partner
Tom S. Pruitt,
Partner
Gregory J. Pusinelli,
Partner
Michael P. Quinn,
Partner
David P. Ricci,		William Blair Funds		Senior Vice President
Partner
Thomas Ross,		Teach Sport Limited		Board Member
Partner
Lisa Rusch,		William Blair Funds		Senior Vice President
Partner
Corey P. Ryan,		Graymatter Holdings, LLC		Board Member
Partner		mHub		Board Member
Alfred J. Salvino,
Partner
John Salvino,
Partner

Name and Position with
William Blair Investment
Management, LLC
and/or William	Name of Company and/or
Blair &Company, L.L.C.	Principal Business	Capacity

Thomas J. Salvino, Partner

Beth Satterfield,

Partner

Craig Savage,

Partner

Ralph E. Schackart, III, Partner

Joe A. Schauenberg, Partner

Matthew Schultz,

Partner

Hugo Scott-Gall,

Partner

Brian F. Scullion,

Partner

Ward D. Sexton,

Partner

Anurag Sharma,

Partner

Andrew J. Siepker,

Partner

Arthur J. Simon,

Partner

Andrew Sims,

Partner

Brian D. Singer,

Partner

Michael M. Sirvinskas, Partner

Michael Siska,

Partner

Jonathan P. Skinner, Partner

Brent M. Smith,

Partner

John S. Sonnier,

Partner

Five Goals LLC

Sole Member

Savage Aviation Inc.

Manager

William Blair Funds

Senior Vice President

William Blair Funds	Trustee
Mitchell Fund	Director
William Blair Funds	Senior Vice President

	Name and Position with
	William Blair Investment
	Management, LLC
	and/or William		Name of Company and/or
	Blair &Company, L.L.C.		Principal Business		Capacity
Rita J. Spitz,
Partner
Per-Ake Stahl,
Partner
Thomas Sternberg,		Tutoring Chicago		Trustee
Partner
Jason Sunderson,
Partner
Bhavanmit S. Suri,
Partner
Dwight Michael Thompson,
Partner
Mark C. Thompson,
Partner
Vivian Lin Thurston,		Xilin Dance Company		Director
Partner		Chinese Finance Association of		Trustee
		America
Samuel J. Tinaglia, Sr.,		Chicago Historical Society		Trustee
Partner		Psi Upsilon Fraternity Philanthropic		President
		Foundation

Corey Tobin,

Partner

Steve Tole,

Partner

Michael Trimberger, Partner

William B. Trukenbrod, Partner

James Gordon Vap II, Partner

Christopher T. Vincent,

Partner

Spiro Voulgaris,

Partner

Michael Ward,

Partner

New Pendulum Corporation d/b/a New Pig

B Drive North Development, LLC

Composite Resources Inc.

Federal Resources Supply Company

Turkey Gap LLC

Economic Freedom Partners LLC

Director

Member

Board Member

Manager

	Name and Position with
	William Blair Investment
	Management, LLC
	and/or William		Name of Company and/or
	Blair &Company, L.L.C.		Principal Business		Capacity
Charles A. Watson,
Partner
Stephen Weeks,
Partner
Brian D. Weinstein,
Partner
Michael F. Wertz,
Partner
James White,
Partner
Kurt M. Wiese,
Partner
James H. Wildman,
Partner
Colin J. Williams,
Partner
Thomas A. Wilson, Jr.,
Partner
Sharon M. Zackfia,
Partner
Matthew M. Zimmer,
Partner
Jon W. Zindel,		Fourth Chakra LLC		Owner/Member
Partner

ITEM 32. Principal Underwriters

(a)Not applicable.

(b)The main business address of each partner and officer of William Blair & Company, L.L.C., principal underwriter for Registrant, is 150 North Riverside Plaza, Chicago, Illinois 60606. Partners of William Blair & Company, L.L.C. may also be partners of William Blair Investment Management, LLC. See Item 31 for information with respect to officers and partners of William Blair & Company, L.L.C. and William Blair Investment Management, LLC.

(c)Not applicable.

ITEM 33. Location of Accounts and Records

All such accounts, books and other documents are maintained by the Registrant's officers at the offices of the Registrant and the offices of the Adviser, William Blair Investment Management, LLC, located at 150 North Riverside Plaza, Chicago, Illinois 60606. Shareholder account information and original shareholder correspondence is also available at the offices of the Transfer Agent and Dividend Paying Agent, DST Asset Manager Solutions, Inc. (formerly Boston Financial Data Services, Inc.), 333 W. 11th Street, Kansas City, Missouri 64105.

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all of the requirements for effectiveness of this registration statement under Rule 485(b) under the Securities Act of 1933 and has duly caused this Post-Effective Amendment No. 133 to the registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Chicago, and State of Illinois, on the 29th day of April, 2020.

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment No. 133 to the registration statement has been signed below by the following persons in the capacity indicated on the 29th day of April, 2020.


Signature		Title

/s/ Arthur J. Simon Arthur J. Simon		Trustee

/s/ Vann A. Avedisian* Vann A. Avedisian		Trustee

/s/ Kathleen T. Barr* Kathleen T. Barr		Trustee

/s/ Daniel N. Leib* Daniel N. Leib		Trustee

/s/ Dorri C. McWhorter* Dorri C. McWhorter		Trustee

/s/ Thomas J. Skelly* Thomas J. Skelly		Trustee

/s/ Steven R. Zenz* Steven R. Zenz		Trustee

/s/ Stephanie G. Braming Stephanie G. Braming		Trustee (Chairman of the Board) and President (Principal Executive Officer)

/s/ John M. Raczek John M. Raczek		Treasurer (Principal Financial Officer, Principal Accounting Officer)

*By: /s/Stephanie G. Braming Stephanie G. Braming, Attorney-in-Fact

* Stephanie G. Braming signs this document pursuant to powers of attorney filed as an exhibit to a previously filed Post-Effective Amendment to the Registrant’s registration statement.

William Blair MAS Ltd. has duly caused this Post-Effective Amendment No. 133 to the registration statement of William Blair Funds, with respect only to information that specifically relates to William Blair MAS Ltd. to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Chicago, and State of Illinois, on the 29th day of April, 2020.

This Post-Effective Amendment No. 133 to the registration statement of William Blair Funds with respect only to information that specifically relates to William Blair MAS Ltd. has been signed below by the following persons in the capacity indicated and on the 29th day of April, 2020.

Written Instrument Establishing and Designating
Class A, B, C, N and I Shares of
the William Blair Tax-Managed Growth Fund, the William Blair Large Cap Growth Fund,
the William Blair Small Cap Growth Fund and the William Blair Disciplined Large Cap Fund

The undersigned, being a majority of the Trustees of the William Blair Funds (the "Trust"), a business trust organized pursuant to a Declaration of Trust dated September 3, 1999 (the "Declaration of Trust"), pursuant to Section 6.2 and Section 6.3 of Article VI of the Declaration of Trust, do hereby establish and designate a seventh, eight, ninth and tenth series of Interests of the Trust to be known as the "William Blair Tax-Managed Growth Fund," the "William Blair Large Cap Growth Fund," the "William Blair Small Cap Growth Fund," and the "William Blair Disciplined Large Cap Fund," respectively (each a "Series"), and further do hereby establish five classes of each Series designated Class A Shares, Class B Shares, Class C Shares, Class N Shares and Class I Shares (each a "Class"). The relative rights and preferences of each such Series and Class shall be as set forth in the Declaration of Trust.

IN WITNESS WHEREOF, the undersigned have this 19th day of October, 1999 signed these presents.

APPENDIX A

MANAGEMENT FEES

William Blair Growth Fund:

.75% of average daily net assets

William Blair Large Cap Growth Fund:

.60% of average daily net assets

William Blair Small Cap Growth Fund:

1.10% of average daily net assets

William Blair International Growth Fund:

1.10% of the first $250 million of average daily net assets; plus 1.00% of the next $2.25 billion of average daily net assets; plus 0.975% of the next $2.5 billion of average daily net assets; plus 0.95% of the next $5 billion of average daily net assets; plus 0.925% of the next $5 billion of average daily net assets; plus 0.90% of the average daily net assets over $15 billion

William Blair Small Cap Value Fund:

0.95% of average daily net assets

William Blair Income Fund:

.25% of the first $250 million of average daily net assets; plus

.20% of average daily net assets over $250 million; plus 5.00% of the gross income earned by the Fund

William Blair Institutional International Growth Fund:

1.00% of the first $500 million of average daily net assets; plus 0.95% of the next $500 million of average daily net assets; plus 0.90% of the next $1.5 billion of average daily net assets; plus 0.875% of the next $2.5 billion of average daily net assets; plus 0.85% of the next $5 billion of average daily net assets; plus 0.825% of the next $5 billion of average daily net assets; plus 0.80% of the average daily net assets over $15 billion

William Blair Small-Mid Cap Growth Fund:

1.00% of average daily net assets

William Blair Emerging Markets Growth Fund:

1.10% of average daily net assets

AMENDMENT (the “Amendment”), effective as of August 1, 2019, by and among WILLIAM BLAIR FUNDS, a Delaware statutory trust (the “Fund”) and STATE STREET BANK AND TRUST COMPANY, a Massachusetts trust company (“State Street”). Capitalized terms used herein without definition shall have the meanings ascribed thereto in the Custodian Agreement (as defined below).

WHEREAS the Fund and Investors Bank & Trust Company (“IBT”) entered into a Custodian Agreement dated October 1, 1999, as amended, modified and supplemented from time to time (the “Custodian Agreement”);

WHEREAS, IBT merged with and into State Street, effective July 2, 2007, with the result that State Street now serves as Custodian under the Custodian Agreement; and

WHEREAS, the Fund and State Street desire to amend the Custodian Agreement as set forth below.

NOW, THEREFORE, in consideration of the premises and of the mutual covenants and agreements herein set forth, the parties hereto agree as follows:

Section 16.1 of the Custodian Agreement is hereby amended by deleting such Section 16.1 in its entirety and by inserting in lieu thereof, the following:

“This Agreement shall remain in effect until July 31, 2020 (the “Term”), unless earlier terminated as provided herein. After the expiration of the Term, this Agreement shall continue until terminated by either party upon one hundred-twenty (120) days prior written notice to the other party.

Either party may terminate this Agreement prior to the expiration of the Term in the event the other party violates any material provision of this Agreement, provided that the non-violating party gives written notice of such violation to the violating party and the violating party does not cure such violation within ninety (90) days of receipt of such notice.”

Appendix A of the Custodian Agreement is hereby amended by deleting such Appendix A in its entirety and by inserting in lieu thereof the attached Appendix A.

Section 18(a) of the Custodian Agreement is hereby amended by deleting such Section 18(a) in its entirety and by inserting in lieu thereof, the following:

Any notice or other instrument in writing authorized or required by this Agreement to be given to either party hereto will be sufficiently given if addressed to such party and delivered via (i) United States Postal Service registered mail, (ii) telecopier with written confirmation, (iii) hand delivered with signature to such party at its office at the address set forth below, namely:

or at such other place as such party may from time to time designate in writing.”

Except as amended hereby, all provisions of the Custodian Agreement shall remain in full force and effect.

This Amendment may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. Counterparts may be executed in either original or electronically transmitted form (e.g., faxes or emailed portable document format (PDF) form), and the parties hereby adopt as original any signatures received via electronically transmitted form.

IN WITNESS WHEREOF, each party hereto has caused this Amendment to be executed by its duly authorized officer, as the case may be, as of the date and year first above written.

FORM OF EXPENSE LIMITATION AGREEMENT

EXPENSE LIMITATION AGREEMENT (the "Agreement"), effective as of May 1, 2020 by and between William Blair Investment Management, LLC, a Delaware limited liability company (the "Adviser") and William Blair Funds, a Delaware statutory trust (the "Trust"), on behalf of each series of the Trust reflected in Schedule A hereto, as may be amended from time to time (each a "Fund" and collectively, the "Funds").

WHEREAS, the Trust, on behalf of each Fund, and the Adviser have entered into a Management Agreement ("Advisory Agreement"), pursuant to which the Adviser provides investment management services to each Fund for compensation based on the value of the average daily net assets of the Fund; and

WHEREAS, each Fund may have one or more classes of shares (each a "Class" and collectively, the "Classes"); and

WHEREAS, the Trust and the Adviser have determined that it is appropriate and in the best interests of each Fund and its shareholders to maintain the Fund's or a Class of the Fund's expenses at a level below the level to which the Fund or Class may otherwise be subject; and

NOW THEREFORE, the parties hereto agree as follows:

1.EXPENSE LIMITATION.

1.1Applicable Expense Limit. To the extent that the ordinary operating expenses incurred by a Fund or a Class of a Fund in any fiscal year, excluding interest expenses, taxes, brokerage commissions, acquired fund fees and expenses, dividend and interest expenses on short sales, other investment-related costs and extraordinary expenses, such as litigation and other expenses not incurred in the ordinary course of a Fund's business ("Operating Expenses"), exceed the percentage of the average daily net assets of a Fund or a Class of a Fund, as set forth in Schedule A (the "Expense Limit"), such excess amount (the "Excess Amount") shall be the liability of the Adviser to the extent set forth in this Agreement. The Trust may offset amounts owed to a Fund or a Class of a Fund pursuant to this Agreement against the advisory fee payable to the Adviser subject to Rule 18f-3 under the Investment Company Act of 1940, as amended (the "1940 Act"). Furthermore, to the extent that the Excess Amount exceeds such waived or reduced investment advisory fees, the Adviser shall reimburse such Fund's or such Class's other Operating Expenses.

1.2Duration of Expense Limit. The Expense Limit with respect to each Fund or Class of a Fund shall remain in effect through the Date of Expiration of Expense Limit as set forth in Schedule A, unless this Agreement is terminated pursuant to Section 3 below.

2.REIMBURSEMENT OF FEE WAIVERS AND EXPENSE REIMBURSEMENTS.

During any of the first three years subsequent to a Fund's commencement of operations, the Adviser shall be entitled to reimbursement by the Fund or a Class of the Fund of the investment advisory fees waived or reduced, and any other expense reimbursements or similar payments

remitted by the Adviser to the Fund or Class pursuant to Section 1 hereof (the "Reimbursement Amount") to the extent that the Fund's or Class's Operating Expenses plus the amount so reimbursed equals the Expense Limit, provided that such amount paid to the Adviser will in no event exceed the total Reimbursement Amount and will not include any amounts previously reimbursed.

3.TERM AND TERMINATION OF AGREEMENT.

This Agreement shall terminate with respect to any Fund or Class of a Fund upon the earlier of termination of the Advisory Agreement or the Date of Expiration of Expense Limit as set forth in Schedule A. The obligation of the Adviser under Section 1 of this Agreement and of the Trust under Section 2 of this Agreement shall survive the termination of the Agreement solely as to expenses and obligations incurred prior to the date of such termination.

4.MISCELLANEOUS.

4.1Captions. The captions in this Agreement are included for convenience of reference only and in no other way define or delineate any of the provisions hereof or otherwise affect their construction or effect.

4.2Interpretation. Nothing herein contained shall be deemed to require the Trust or a

Fund to take any action contrary to the Trust's Declaration of Trust or By-Laws, or any applicable statutory or regulatory requirement to which it is subject or by which it is bound, or to relieve or deprive the Trust's Board of Trustees of its responsibility for and control of the conduct of the affairs of the Trust or a Fund.

4.3Definitions. Any question of interpretation of any term or provision of this Agreement, including but not limited to the investment advisory fee, the computations of net asset values, and the allocation of expenses, having a counterpart in or otherwise derived from the terms and provisions of the Advisory Agreement or the 1940 Act, shall have the same meaning as and be resolved by reference to such Advisory Agreement or the 1940 Act.

4.4Amendments. This Agreement may be amended only by a written agreement signed by each of the parties hereto.

4.5Limitation of Liability. This Agreement is executed by or on behalf of the Trust, and the Adviser is hereby expressly put on notice of the limitation of shareholder liability as set forth in the Agreement and Declaration of Trust, as amended, of the Trust and agrees that the obligations assumed by the Trust pursuant to this Agreement shall be limited in all cases to the Trust and its assets, and the Adviser shall not seek satisfaction of any such obligations from the trustees, officers or shareholders of the Trust.

SCHEDULE A

(as of May 1, 2020)

		Date of
	Expense	Expiration of
Fund	Limit (%)	Expense Limit
William Blair Growth Fund
Class N	1.20%	4/30/2021
Class I	0.95%	4/30/2021
Class R6	0.90%	4/30/2021
William Blair Large Cap Growth Fund
Class N	0.90%	4/30/2021
Class I	0.65%	4/30/2021
Class R6	0.60%	4/30/2021
William Blair Mid Cap Growth Fund

Class N	1.20%	4/30/2021
Class I	0.95%	4/30/2021
Class R6	0.90%	4/30/2021
William Blair Small-Mid Cap Core Fund

Class I	0.95%	4/30/2021
Class R6	0.90%	4/30/2021
William Blair Small-Mid Cap Growth Fund

Class N	1.35%	4/30/2021
Class I	1.10%	4/30/2021
Class R6	1.05%	4/30/2021
William Blair Small-Mid Cap Value Fund

Class N	1.15%	4/30/2021
Class I	0.90%	4/30/2021
Class R6	0.85%	4/30/2021
William Blair Small Cap Growth Fund

Class N	1.50%	4/30/2021
Class I	1.25%	4/30/2021
Class R6	1.20%	4/30/2021
William Blair Small Cap Value Fund

Class N	1.25%	4/30/2021
Class I	1.00%	4/30/2021
Class R6	0.95%	4/30/2021
William Blair Global Leaders Fund

Class N	1.15%	4/30/2021
Class I	0.90%	4/30/2021
Class R6	0.85%	4/30/2021
William Blair International Leaders Fund

Class N	1.15%	4/30/2021
Class I	0.90%	4/30/2021
Class R6	0.85%	4/30/2021

William Blair International Growth Fund
Class N	1.45%	4/30/2021
Class I	1.20%	4/30/2021
Class R6	1.15%	4/30/2021
William Blair Institutional International Growth Fund	1.05%	4/30/2021
William Blair International Small Cap Growth Fund
Class N	1.55%	4/30/2021
Class I	1.30%	4/30/2021
Class R6	1.25%	4/30/2021
William Blair Emerging Markets Leaders Fund

Class N	1.40%	4/30/2021
Class I	1.15%	4/30/2021
Class R6	1.10%	4/30/2021
William Blair Emerging Markets Growth Fund

Class N	1.60%	4/30/2021
Class I	1.35%	4/30/2021
Class R6	1.30%	4/30/2021
William Blair Emerging Markets Small Cap Growth Fund

Class N	1.55%	4/30/2021
Class I	1.30%	4/30/2021
Class R6	1.25%	4/30/2021
William Blair Bond Fund

Class N	0.60%	4/30/2021
Class I	0.45%	4/30/2021
Class R6	0.40%	4/30/2021
William Blair Income Fund

Class N	0.85%	4/30/2021
Class I	0.70%	4/30/2021
Class R6	0.65%	4/30/2021
William Blair Low Duration Fund

Class N	0.55%	4/30/2021
Class I	0.40%	4/30/2021
Class R6	0.35%	4/30/2021
William Blair Macro Allocation Fund
Class N	1.25%	4/30/2021
Class I	1.00%	4/30/2021
Class R6	0.95%	4/30/2021

This Amendment (the “Amendment”), effective as of August 1, 2019, by and among WILLIAM BLAIR FUNDS, a Delaware statutory trust (the “Fund”) and STATE STREET BANK AND TRUST COMPANY, a Massachusetts trust company (“State Street”). Capitalized terms used herein without definition shall have the meanings ascribed thereto in the Administration Agreement (as defined below).

WHEREAS the Fund and Investors Bank & Trust Company (“IBT”) entered into an Administration Agreement dated November 1, 2004, as amended, modified and supplemented from time to time (the “Administration Agreement”);

WHEREAS, IBT merged with and into State Street, effective July 2, 2007, with the result that State Street now serves as Administrator under the Administration Agreement; and

WHEREAS, the Fund and State Street desire to amend the Administration Agreement as set forth below.

NOW, THEREFORE, in consideration of the premises and of the mutual covenants and agreements herein set forth, the parties hereto agree as follows:

Section 7(a) of the Administration Agreement is hereby amended by deleting such Section 7(a) in its entirety and by inserting in lieu thereof, the following:

Appendix A of the Administration Agreement is hereby amended by deleting such Appendix A in its entirety and by inserting in lieu thereof the attached Appendix A.

Section 8 (a) of the Administration Agreement is hereby amended by deleting such Section 8 (a) in its entirety and by inserting in lieu thereof, the following:

(a) Any notice or other instrument authorized or required by this Agreement to be given in writing to the Fund or the Bank shall be sufficiently given if addressed to that party and received by it at its office set forth below or at such other place as it may from time to time designate in writing.

Except as amended hereby, all provisions of the Administration Agreement shall remain in full force and effect.

IN WITNESS WHEREOF, each party hereto has caused this Amendment to be executed by its duly authorized officer, as the case may be, as of the date and year first above written.

We have acted as counsel for William Blair Funds (the “Trust”), a Delaware statutory trust, in connection with the filing of Post-Effective Amendment No. 133 to the Trust’s registration statement on Form N-1A under the Securities Act of 1933, as amended (the “1933 Act”), and Amendment No. 134 under the Investment Company Act of 1940, as amended (the “Registration Statement”), relating to the issuance and sale by the Trust of its authorized shares, currently divided into several Series and Classes.

This opinion is limited to the Delaware Statutory Trust Act statute, and we express no opinion with respect to the laws of any other jurisdiction or to any other laws of the State of Delaware. Further, we express no opinion as to compliance with any state or federal securities laws, including the securities laws of the State of Delaware.

In connection with the opinions set forth herein, we have examined the following documents: the Trust’s Declaration of Trust dated September 3, 1999, as amended to date; the Trust’s Amended and Restated By-Laws dated February 2, 2018; and such other Trust records, certificates, resolutions, documents and statutes that we have deemed relevant in order to render the opinions expressed herein. In addition, we have reviewed and relied upon the certificate referred to below issued by the Delaware Secretary of State.

In rendering this opinion we have assumed, without independent verification, (i) the due authority of all individuals signing in representative capacities and the genuineness of signatures; (ii) the authenticity, completeness and continued effectiveness of all documents or copies furnished to us; (iii) that any resolutions provided have been duly adopted by the Trust’s Board of Trustees; (iv) that the facts contained in the instruments and certificates or statements of public officials, officers and representatives of the Trust on which we have relied for the purposes of this opinion are true and correct; and (v) that no amendments, agreements, resolutions or actions have been approved, executed or adopted which would limit, supersede or modify the items described above. Where documents are referred to in resolutions approved by the Board of Trustees, or in the Registration Statement, we have assumed such documents are the same as in the most recent form provided to us, whether as an exhibit to the Registration Statement or otherwise.

Based upon the foregoing, we are of the opinion that the shares of the Series and each Class have been duly authorized for issuance and, when issued and delivered against payment therefor in accordance with the terms, conditions, requirements and procedures described in the Registration Statement, will be validly issued and, subject to the qualifications set forth in the Declaration of Trust, fully paid and non-assessable beneficial interests in such Series and Class.

In rendering the opinion above, insofar as it relates to the valid existence of the Trust, we have relied solely on a certificate of the Secretary of State of the State of Delaware, dated April 27, 2020, and such opinion is limited accordingly and is rendered as of the date of such certificate.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement, to be filed with the Securities and Exchange Commission, and to the use of our name in the Registration Statement. In giving such consent, however, we do not admit that we are within the category of persons whose consent is required by Section 7 of the 1933 Act or the rules and regulations thereunder.

We consent to the reference to our firm under the captions “Financial Highlights” in each Prospectus and “Independent Registered Public Accounting Firm” in the Statement of Additional Information and to the incorporation by reference of our report dated February 26, 2020, for Growth Fund, Large Cap Growth Fund, Mid Cap Growth Fund, Small-Mid Cap Core Fund, Small-Mid Cap Growth Fund, Small-Mid Cap Value Fund, Small Cap Growth Fund, Small Cap Value Fund, Global Leaders Fund, International Leaders Fund, International Growth Fund, Institutional International Growth Fund, International Small Cap Growth Fund, Emerging Markets Leaders Fund, Emerging Markets Growth Fund, Emerging Markets Small Cap Growth Fund, Bond Fund, Income Fund, Low Duration Fund and Macro Allocation Fund (the Funds comprising the William Blair Funds) in the Registration Statement (Form N-1A) of William Blair Funds filed with the Securities and Exchange Commission in this Post-Effective Amendment No. 133 to the Registration Statement under the Securities Act of 1933 (Registration No. 33-17463).


U.S. Equity Funds	Class N	Class I	Class R6
Growth Fund	WBGSX	BGFIX	BGFRX
Large Cap Growth Fund	LCGNX	LCGFX	LCGJX
Mid Cap Growth Fund	WCGNX	WCGIX	WCGJX
Small-Mid Cap Core Fund	—	WBCIX	WBCRX
Small-Mid Cap Growth Fund	WSMNX	WSMDX	WSMRX
Small-Mid Cap Value Fund	BSMNX	WSMIX	BSMRX
Small Cap Growth Fund	WBSNX	WBSIX	WBSRX
Small Cap Value Fund	WBVDX	BVDIX	BVDRX

Global/International Funds	Class N	Class I	Class R6
Global Leaders Fund	WGGNX	WGFIX	BGGIX
International Leaders Fund	WILNX	WILIX	WILJX
International Growth Fund	WBIGX	BIGIX	WBIRX
Institutional International Growth Fund (WBIIX)	—	—	—
International Small Cap Growth Fund	WISNX	WISIX	WIISX
Emerging Markets Leaders Fund	WELNX	WBELX	WELIX
Emerging Markets Growth Fund	WBENX	WBEIX	BIEMX
Emerging Markets Small Cap Growth Fund	WESNX	BESIX	WESJX

Fixed Income Funds	Class N	Class I	Class R6
Bond Fund	WBBNX	WBFIX	BBFIX
Income Fund	WBRRX	BIFIX	BIFJX
Low Duration Fund	WBLNX	WBLIX	WBLJX


Summary			1

William Blair Growth Fund			1

William Blair Large Cap Growth Fund			6

William Blair Mid Cap Growth Fund			11

William Blair Small-Mid Cap Core Fund			16

William Blair Small-Mid Cap Growth Fund			20

William Blair Small-Mid Cap Value Fund			25

William Blair Small Cap Growth Fund			30

William Blair Small Cap Value Fund			35

William Blair Global Leaders Fund			40

William Blair International Leaders Fund			46

William Blair International Growth Fund			52

William Blair Institutional International Growth Fund			57

William Blair International Small Cap Growth Fund			62

William Blair Emerging Markets Leaders Fund			67

William Blair Emerging Markets Growth Fund			73

William Blair Emerging Markets Small Cap Growth Fund			78

William Blair Bond Fund			84

William Blair Income Fund			89

William Blair Low Duration Fund			94

Additional Information Regarding Investment Objectives and Strategies			99

Principal Risks			101

Management of the Funds			109

Your Account			117

Class N Shares			117

Class I Shares			117

Class R6 Shares			118

Additional Information and Exceptions to Eligibility and Minimum Investment Requirements for Class N, Class I and Class R6 Shares			119

Additional Information for Class N Shares			119

Additional Information on Other Payments to Financial Intermediaries			120

International Growth Fund, Institutional International Growth Fund, International Small Cap Growth Fund and Emerging Markets Small Cap Growth Fund			120

Buying, Selling and Exchanging Shares			121

How to Buy Shares			121

How to Sell Shares			124

How to Exchange Shares			126

Dividends and Distributions			127

Federal Income Taxes			127

Shareholder Services and Account Policies			130

Determination of Net Asset Value			133

Investment Glossary			135

Financial Highlights			141

For More Information			177


	Class N		Class I		Class R6
Management Fee		0.75%		0.75%		0.75%
Distribution (Rule 12b-1) Fee		0.25%		None		None
Other Expenses		0.24%		0.17%		0.13%

Total Annual Fund Operating Expenses		1.24%		0.92%		0.88%
Fee Waiver and/or Expense Reimbursement*		0.04%		N/A		N/A

Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement		1.20%		0.92%		0.88%


	1 Year	3 Years	5 Years	10 Years
Class N	$122	$389	$677	$1,496
Class I	94	293	509	1,131
Class R6	90	281	488	1,084


	1 Year		5 Years		10 Years
Class N Shares
Return Before Taxes		31.97%		12.46%		12.85%
Return After Taxes on Distributions		28.97%		7.91%		9.79%
Return After Taxes on Distributions and Sale of Fund Shares		20.95%		9.02%		9.98%

Class I Shares
Return Before Taxes		32.32%		12.78%		13.19%

*Russell 3000^® Growth Index* (reflects no deduction for fees, expenses or taxes)		35.85%		14.23%		15.05%
*S&P 500^® Index* (reflects no deduction for fees, expenses or taxes)		31.49%		11.70%		13.56%


	Class I		Class R6
Maximum Sales Charge (Load) Imposed on Purchases		None		None
Redemption Fee		None		None


	1 Year		5 Years		Life of the Fund (since December 15, 2011)
Class N Shares
Return Before Taxes		22.77%		5.90%		10.44%
Return After Taxes on Distributions		22.26%		3.55%		8.02%
Return After Taxes on Distributions and Sale of Fund Shares		13.83%		4.30%		7.87%

Class I Shares
Return Before Taxes		23.00%		6.17%		10.73%

*Russell 2500^TM Value Index* (reflects no deduction for fees, expenses or taxes)		23.56%		7.18%		12.11%


	1 Year		5 Years		Since Share Class Inception (December 19, 2012)
Class R6 Shares
Return Before Taxes		32.02%		10.54%		10.96%

*MSCI All Country World IMI (net)* (reflects no deduction for fees, expenses or taxes)		26.35%		8.34%		9.62%


	1 Year		5 Years		Life of the Fund (since August 16, 2012)
Class N Shares
Return Before Taxes		31.46%		9.74%		9.77%
Return After Taxes on Distributions		31.36%		9.35%		9.42%
Return After Taxes on Distributions and Sale of Fund Shares		18.70%		7.65%		7.83%

Class I Shares
Return Before Taxes		31.76%		10.00%		10.04%

*MSCI All Country World Ex-US IMI (net)* (reflects no deduction for fees, expenses or taxes)		21.63%		5.71%		6.56%


	1 Year		5 Years		Since Share Class Inception (November 2, 2012)
Class R6 Shares
Return Before Taxes		31.83%		10.10%		10.10%

*MSCI All Country World Ex-US IMI (net)* (reflects no deduction for fees, expenses or taxes)		21.63%		5.71%		6.20%


Management Fee			0.94%
Distribution (Rule 12b-1) Fee			None
Other Expenses			0.05%

Total Annual Fund Operating Expenses			0.99%


	1 Year		5 Years		Since Share Class Inception (May 3, 2010)
Class N Shares
Return Before Taxes		27.98%		5.27%		4.31%

*MSCI Emerging Markets Index (net)* (reflects no deduction for fees, expenses or taxes)		18.42%		5.61%		3.54%


	1 Year		5 Years		Life of the Fund (since October 24, 2011)
Class N Shares
Return Before Taxes		20.34%		2.69%		8.74%
Return After Taxes on Distributions		20.34%		2.00%		8.14%
Return After Taxes on Distributions and Sale of Fund Shares		12.04%		1.89%		6.94%

Class I Shares
Return Before Taxes		20.58%		2.99%		9.05%

*MSCI Emerging Markets Small Cap Index (net)* (reflects no deduction for fees, expenses or taxes)		11.50%		2.97%		3.76%


	1 Year		5 Years		Since Share Class Inception (December 20, 2012)
Class R6 Shares
Return Before Taxes		20.69%		3.07%		6.77%

*MSCI Emerging Markets Small Cap Index (net)* (reflects no deduction for fees, expenses or taxes		11.50%		2.97%		2.60%


Fund	Fee as a % of Average Daily Net Assets
Growth Fund		0.75%
Large Cap Growth Fund		0.60%	⁽¹⁾
Mid Cap Growth Fund		0.90%	⁽²⁾
Small-Mid Cap Core Fund		0.90%
Small-Mid Cap Growth Fund		1.00%
Small-Mid Cap Value Fund		0.85%	⁽³⁾
Small Cap Growth Fund		1.10%
Small Cap Value Fund		0.95%	⁽⁴⁾
Global Leaders Fund		0.85%	⁽ ⁵ ⁾
International Leaders Fund		0.85%	⁽ ⁶ ⁾
International Growth Fund		1.01%	⁽⁷⁾
Institutional International Growth Fund		0.94%	⁽ ⁸ ⁾
International Small Cap Growth Fund		1.00%
Emerging Markets Leaders Fund		1.10%
Emerging Markets Growth Fund		1.10%
Emerging Markets Small Cap Growth Fund		1.10%
Bond Fund		0.30%
Income Fund		0.40%	⁽ ⁹ ⁾
Low Duration Fund		0.30%


	Class N		Class I		Class R6/ Institutional Fund
Growth Fund		1.20%		0.95%		0.90%
Large Cap Growth Fund		0.90%		0.65%		0.60%
Mid Cap Growth Fund		1.20%		0.95%		0.90%
Small-Mid Cap Core Fund		N/A		0.95%		0.90%
Small-Mid Cap Growth Fund		1.35%		1.10%		1.05%
Small-Mid Cap Value Fund		1.15%		0.90%		0.85%
Small Cap Growth Fund		1.50%		1.25%		1.20%
Small Cap Value Fund		1.25%		1.00%		0.95%
Global Leaders Fund		1.15%		0.90%		0.85%
International Leaders Fund		1.15%		0.90%		0.85%
International Growth Fund		1.45%		1.20%		1.15%
Institutional International Growth Fund		N/A		N/A		1.05%
International Small Cap Growth Fund		1.55%		1.30%		1.25%
Emerging Markets Leaders Fund		1.40%		1.15%		1.10%
Emerging Markets Growth Fund		1.60%		1.35%		1.30%
Emerging Markets Small Cap Growth Fund		1.55%		1.30%		1.25%
Bond Fund		0.60%		0.45%		0.40%
Income Fund		0.85%		0.70%		0.65%
Low Duration Fund		0.55%		0.40%		0.35%


Average Annual Total Returns For the Periods Ended December 31, 2019	1 Year			Since Inception (June 1, 2017)
SMID Core Composite
Net of Fees—Class I*		28.48	%		12.38	%
Net of Fees—Class R6*		25.55	%		11.32	%
Gross of Fees		29.68	%		11.38	%
Russell 2500^TM Index** (reflects no deductions for fees, expenses or taxes)		27.77	%		10.66	%


	Class N
	Years Ended December 31,
	2019			2018			2017			2016			2015
Net asset value, beginning of year	$	7.91		$	10.27		$	11.41		$	12.52		$	13.55
Income (loss) from investment operations:
Net investment income (loss)		(0.03	)		(0.04	)		(0.02	)		(0.02	)		(0.04	)
Net realized and unrealized gain (loss) on investments		2.54			0.75			2.78			(0.08	)		0.75

Total from investment operations		2.51			0.71			2.76			(0.10	)		0.71
Less distributions from:
Net investment income		—			—			—			—			—
Net realized gain		0.97			3.07			3.90			1.01			1.74

Total distributions		0.97			3.07			3.90			1.01			1.74

Net asset value, end of year	$	9.45		$	7.91		$	10.27		$	11.41		$	12.52

Total return (%)		31.97			5.10			24.35			(0.98	)		5.31
Ratios to average daily net assets (%):
Expenses, before waivers and reimbursements.		1.24			1.22			1.20			1.21			1.19
Expenses, net of waivers and reimbursements		1.20			1.20			1.20			1.21			1.19
Net investment income (loss), before waivers and reimbursements		(0.35	)		(0.36	)		(0.14	)		(0.15	)		(0.29	)
Net investment income (loss), net of waivers and reimbursements		(0.31	)		(0.34	)		(0.14	)		(0.15	)		(0.29	)
Class N net assets at the end of the year (in thousands)	$	32,710		$	38,370		$	34,886		$	62,936		$	149,754
Portfolio turnover rate (%)		39			46			38			79			78

	Class I
	Years Ended December 31,
	2019			2018			2017			2016			2015
Net asset value, beginning of year	$	9.25		$	11.51		$	12.39		$	13.50		$	14.43
Income (loss) from investment operations:
Net investment income (loss)		(0.00	)^		(0.01	)		0.02			0.03			0.01
Net realized and unrealized gain (loss) on investments		2.97			0.82			3.02			(0.10	)		0.80

Total from investment operations		2.97			0.81			3.04			(0.07	)		0.81
Less distributions from:
Net investment income		—			0.00	^		0.02			0.03			—
Net realized gain		0.97			3.07			3.90			1.01			1.74

Total distributions		0.97			3.07			3.92			1.04			1.74

Net asset value, end of year	$	11.25		$	9.25		$	11.51		$	12.39		$	13.50

Total return (%)		32.32			5.42			24.64			(0.69	)		5.69
Ratios to average daily net assets (%):
Expenses		0.92			0.91			0.92			0.90			0.89
Net investment income (loss)		(0.03	)		(0.06	)		0.12			0.20			0.06
Class I net assets at the end of the year (in thousands)	$	220,660		$	187,306		$	318,848		$	514,870		$	696,744
Portfolio turnover rate (%)		39			46			38			79			78


	Class R6
	Period Ended December 31,
	2019(a)
Net asset value, beginning of year	$	11.06
Income (loss) from investment operations:
Net investment income (loss)		(0.00	)^
Net realized and unrealized gain (loss) on investments		1.17

Total from investment operations		1.17
Less distributions from:
Net investment income		—
Net realized gain		0.97

Total distributions		0.97

Net asset value, end of year	$	11.26

Total return (%)*		10.75
Ratios to average daily net assets (%)**:
Expenses		0.88
Net investment income (loss)		(0.06	)
Class R6 net assets at the end of the year (in thousands)	$	217
Portfolio turnover rate (%)*		39


	Institutional
	Years Ended December 31,
	2019		2018			2017		2016			2015
Net asset value, beginning of year	$	13.40	$	18.08		$	14.55	$	15.08		$	15.26
Income (loss) from investment operations:
Net investment income (loss)		0.12		0.18			0.21		0.18			0.19
Net realized and unrealized gain (loss) on investments		4.00		(3.29	)		4.07		(0.54	)		(0.18	)

Total from investment operations		4.12		(3.11	)		4.28		(0.36	)		0.01
Less distributions from:
Net investment income		0.17		0.17			0.44		0.17			0.09
Net realized gain		—		1.40			0.31		—			0.10

Total distributions		0.17		1.57			0.75		0.17			0.19

Net asset value, end of year	$	17.35	$	13.40		$	18.08	$	14.55		$	15.08

Total return (%)		30.75		(17.50	)		29.53		(2.40	)		0.09
Ratios to average daily net assets (%):
Expenses		0.99		0.97			0.97		0.98			0.96
Net investment income (loss),.		0.77		1.01			1.22		1.25			1.18
Net assets at the end of the year (in thousands)	$	1,892,911	$	1,784,435		$	2,330,299	$	2,093,971		$	2,335,632
Portfolio turnover rate (%)		35		82			84		105			70


U.S. EQUITY		GLOBAL/INTERNATIONAL EQUITY
Growth Fund		Global Leaders Fund
Large Cap Growth Fund		International Leaders Fund
Mid Cap Growth Fund		International Growth Fund
Small-Mid Cap Core Fund		Institutional International Growth Fund
Small-Mid Cap Growth Fund		International Small Cap Growth Fund
Small-Mid Cap Value Fund		Emerging Markets Leaders Fund
Small Cap Growth Fund		Emerging Markets Growth Fund
Small Cap Value Fund		Emerging Markets Small Cap Growth Fund

FIXED INCOME
Bond Fund
Income Fund
Low Duration Fund


	1 Year		5 Years		Life of the Fund (since November 29, 2011)
Class N Shares
Return Before Taxes		3.97%		0.62%		4.27%
Return After Taxes on Distributions		2.67%		0.05%		3.30%
Return After Taxes on Distributions and Sale of Fund Shares		2.56%		0.22%		2.97%

Class I Shares
Return Before Taxes		4.14%		0.88%		4.53%

*ICE BofAML US* 3-*Month* *Treasury Bill Index* (reflects no deduction for fees, expenses or taxes)		2.28%		1.07%		0.69%


	1 Year		5 Years		Since Share Class Inception (October 21, 2013)
Class R6 Shares
Return Before Taxes		4.29%		0.99%		1.58%

*ICE BofAML US* 3-*Month* *Treasury Bill Index* (reflects no deduction for fees, expenses or taxes)		2.28%		1.07%		0.87%


	Page
MANAGEMENT OF THE TRUST		1

Investment Adviser.		1
Distributor		11
Other Payments to Third Parties and Affiliates		13
Code of Ethics		14
Proxy Voting Policy		14
Trustees and Officers		15
Board of Trustees		21
Trustee Qualifications		22
Trustee Compensation		24
Trustees’ and Officers’ Holdings of Fund Shares		24
Trustees’ Holdings in Certain Affiliates of the Adviser		25
Principal Shareholders		26
Brokerage and Fund Transactions		46
Disclosure of Portfolio Holdings		50

INVESTMENT POLICIES AND RESTRICTIONS		51

INVESTMENT PRACTICES AND RISKS		55

Borrowings		55
Business Development Companies (“BDCs”)		55
Collateralized Obligations		55
Convertible Securities		60
Derivative Instruments		61
Equity Securities		72
Exchange-Traded Notes		72
Fixed Income Securities		72
Foreign Securities		73
Forward Foreign Currency Transactions		78
Foreign Currency Futures		79
High-Yield/High-Risk Securities		79
Hybrid Bonds		80
Illiquid Securities		80
Investment Companies (each Fund except the Macro Allocation Fund)		80
Investment Companies (Macro Allocation Fund)		81
Lending		83
Limited Liability Companies (“LLCs”)		83
Market Conditions and Events		83
New Companies		83
Publicly Traded Partnerships		84
Real Estate Investment Trusts (“REITs”)		84
Repurchase Agreements		85
Restricted Securities		85
Reverse Repurchase Agreements		85
Royalty Income Trusts		85
Section 4(a)(2) Paper		86
Short Sales		86
Short-Term Trading		86
Small Companies		87


	Page
Special Purpose Acquisition Companies		87
Temporary Defensive Position		87
U.S. Government Securities		87
Variable Rate Securities		88
Warrants		88
When-Issued or Delayed Delivery Transactions		89

ADDITIONAL INFORMATION ABOUT THE FUNDS		89

General		89
Summary of Fees Paid to William Blair for Class N Shares		90
Summary of Fees Paid to William Blair for Class I Shares		90
Summary of Fees Paid to William Blair for Class R6 Shares and Institutional Funds		90
Share Certificates		90
Suspension of Redemption or Delay in Payment		91
Special Redemptions		91
Exchange Privileges		91
Conversion Privilege		91

GENERAL TRUST INFORMATION		92

Determination of Net Asset Value		92
Federal Income Tax Matters		93
Independent Registered Public Accounting Firm		101
Custodian		101
Transfer Agent Services		101
Reports to Shareholders		101

SHAREHOLDER RIGHTS		101

Derivative Claims of Shareholders		102
Forum for Adjudication of Disputes		102

TRUST HISTORY		103

FINANCIAL INFORMATION OF THE TRUST		103

APPENDIX A - RATINGS OF DEBT OBLIGATIONS		A-1


	% of Average Daily Net Assets
Growth Fund		0.75	%
Large Cap Growth Fund		0.60	%
Mid Cap Growth Fund		0.90	%
Small-Mid Cap Core Fund		0.90	%
Small-Mid Cap Growth Fund		1.00	%
Small-Mid Cap Value Fund		0.85	%
Small Cap Growth Fund		1.10	%
Small Cap Value Fund		0.95	%
Global Leaders Fund		0.85	%
International Leaders Fund		0.85	%
International Growth Fund:
First $250 million		1.10	%
Next $2.25 billion		1.00	%
Next $2.5 billion		0.975	%
Next $5 billion		0.95	%
Next $5 billion		0.925	%
In excess of $15 billion		0.90	%
Institutional International Growth Fund:
First $500 million		1.00	%
Next $500 million		0.95	%
Next $1.5 billion		0.90	%
Next $2.5 billion		0.875	%
Next $5 billion		0.85	%
Next $5 billion		0.825	%
In excess of $15 billion		0.80	%
International Small Cap Growth Fund		1.00	%
Emerging Markets Leaders Fund		1.10	%
Emerging Markets Growth Fund		1.10	%
Emerging Markets Small Cap Growth Fund		1.10	%
Bond Fund		0.30	%
Income Fund:⁽¹⁾
First $250 million		0.25	%
In excess of $250 million		0.20	%
Low Duration Fund		0.30	%
Macro Allocation Fund		0.80	%


	Class N			Class I			Class R6/ Institutional Funds
Growth Fund		1.20	%		0.95	%		0.90	%
Large Cap Growth Fund		0.90	%		0.65	%		0.60	%
Mid Cap Growth Fund		1.20	%		0.95	%		0.90	%
Small-Mid Cap Core Fund		N/A			0.95	%		0.90	%
Small-Mid Cap Growth Fund		1.35	%		1.10	%		1.05	%
Small-Mid Cap Value Fund		1.15	%		0.90	%		0.85	%
Small Cap Growth Fund		1.50	%		1.25	%		1.20	%
Small Cap Value Fund		1.25	%		1.00	%		0.95	%
Global Leaders Fund		1.15	%		0.90	%		0.85	%
International Leaders Fund		1.15	%		0.90	%		0.85	%
International Growth Fund		1.45	%		1.20	%		1.15	%
Institutional International Growth Fund		N/A			N/A			1.05	%
International Small Cap Growth Fund		1.55	%		1.30	%		1.25	%
Emerging Markets Leaders Fund		1.40	%		1.15	%		1.10	%
Emerging Markets Growth Fund		1.60	%		1.35	%		1.30	%
Emerging Markets Small Cap Growth Fund		1.55	%		1.30	%		1.25	%
Bond Fund		0.60	%		0.45	%		0.40	%
Income Fund		0.85	%		0.70	%		0.65	%
Low Duration Fund		0.55	%		0.40	%		0.35	%
Macro Allocation Fund		1.25	%		1.00	%		0.95	%


2019	Gross Management Fee		Management Fee Waiver		Net Management Fee		Expenses Reimbursed
Growth Fund	$	1,900,656	$	17,115	$	1,883,541	$	—
Large Cap Growth Fund⁽¹⁾		1,425,637		284,463		1,141,174		—
Mid Cap Growth Fund⁽²⁾		619,173		221,424		397,749		—
Small-Mid Cap Core Fund⁽³⁾		12,301		12,301		—		28,873
Small-Mid Cap Growth Fund		27,928,384		1,727,358		26,201,026		—
Small-Mid Cap Value Fund⁽⁴⁾		28,585		28,585		—		132,777
Small Cap Growth Fund		7,523,027		158,072		7,364,955		—
Small Cap Value Fund		5,168,174		257,980		4,910,194		—
Global Leaders Fund⁽⁵⁾		1,666,280		222,745		1,443,535		—
International Leaders Fund⁽⁶⁾		4,622,006		319,270		4,302,736		—
International Growth Fund		21,323,153		19,455		21,303,698		—
Institutional International Growth Fund		17,129,204		—		17,129,204		—
International Small Cap Growth Fund		3,166,314		—		3,166,314		—
Emerging Markets Leaders Fund		2,429,790		195,464		2,234,326		—
Emerging Markets Growth Fund		8,749,971		—		8,749,971		—
Emerging Markets Small Cap Growth Fund		3,085,400		266,238		2,819,162		—


Type of Account	Number		Total Assets		Number Charged Performance Fee		Total Assets Charged Performance Fees
Registered investment companies		0	$	—		0	$	0
Other pooled investment vehicles		3		80,718,833		0		0
Other advisory accounts		20		870,121,592		0		0


Portfolio Manager	Name of Fund	Dollar Range of Shares Owned
David C. Fording	Growth Fund	$500,001-$1,000,000
James S. Golan	Large Cap Growth Fund	Over $1 Million
David P. Ricci	Large Cap Growth Fund	Over $1 Million
Daniel Crowe	Mid Cap Growth Fund	$500,001-$1,000,000
James E. Jones	Mid Cap Growth Fund	$100,001-$500,000
Robert C. Lanphier IV	Mid Cap Growth Fund	$500,001-$1,000,000
Daniel Crowe	Small-Mid Cap Core Fund	Over $1 Million
Robert C. Lanphier IV	Small-Mid Cap Core Fund	$500,001-$1,000,000
Ward D. Sexton	Small-Mid Cap Core Fund	Over $1 Million
Daniel Crowe	Small-Mid Cap Growth Fund	Over $1 Million
James E. Jones	Small-Mid Cap Growth Fund	$100,001-$500,000
Robert C. Lanphier IV	Small-Mid Cap Growth Fund	$500,001-$1,000,000
Chad M. Kilmer	Small-Mid Cap Value Fund	$100,001-$500,000
Mark T. Leslie	Small-Mid Cap Value Fund	$100,001-$500,000
David S. Mitchell	Small-Mid Cap Value Fund	$100,001-$500,000
Michael P. Balkin	Small Cap Growth Fund	Over $1 Million
Ward D. Sexton	Small Cap Growth Fund	$100,001-$500,000
Chad M. Kilmer	Small Cap Value Fund	$100,001-$500,000
Mark T. Leslie	Small Cap Value Fund	$500,001-$1,000,000
David S. Mitchell	Small Cap Value Fund	Over $1 Million
Andrew G. Flynn	Global Leaders Fund	$100,001-$500,000
Kenneth J. McAtamney	Global Leaders Fund	Over $1 Million
Simon Fennell	International Leaders Fund	$50,001-$100,000
Kenneth J. McAtamney	International Leaders Fund	Over $1 Million
Simon Fennell	International Growth Fund	$50,001-$100,000
Kenneth J. McAtamney	International Growth Fund	$500,001-$1,000,000
Simon Fennell	Institutional International Growth Fund	None
Kenneth J. McAtamney	Institutional International Growth Fund	$500,001-$1,000,000
Simon Fennell	International Small Cap Growth Fund	$100,001-$500,000
Andrew G. Flynn	International Small Cap Growth Fund	$500,001-$1,000,000
Todd M. McClone	Emerging Markets Leaders Fund	$100,001-$500,000
John C. Murphy	Emerging Markets Leaders Fund	Over $1 Million
Todd M. McClone	Emerging Markets Growth Fund	$100,001-$500,000
Casey Preyss	Emerging Markets Growth Fund	$500,001-$1,000,000
Todd M. McClone	Emerging Markets Small Cap Growth Fund	Over $1 Million
Casey Preyss	Emerging Markets Small Cap Growth Fund	$100,001-$500,000
Paul J. Sularz	Bond Fund	$100,001-$500,000
Ruta Ziverte*	Bond Fund	None
Ruta Ziverte*	Income Fund	None
Paul J. Sularz	Low Duration Fund	$100,001-$500,000
Kathleen M. Lynch*	Low Duration Fund	$1-$10,000
Thomas Clarke	Macro Allocation Fund	$100,001-$500,000
Brian D. Singer	Macro Allocation Fund	Over $1 Million


	Rule 12b-1 Fee
Growth Fund	$	96,649
Large Cap Growth Fund		139,221
Mid Cap Growth Fund		14,157
Small-Mid Cap Growth Fund		904,967
Small-Mid Cap Value Fund		648
Small Cap Growth Fund		482,219
Small Cap Value Fund		40,199
Global Leaders Fund		20,550
International Leaders Fund		25,268
International Growth Fund		1,221,233
International Small Cap Growth Fund		8,828
Emerging Markets Leaders Fund		5,598
Emerging Markets Growth Fund		19,231
Emerging Markets Small Cap Growth Fund		14,249
Bond Fund		81,480
Income Fund		31,990
Low Duration Fund		2,477
Macro Allocation Fund		80,356


	Compensation to Financial Services Firms
Growth Fund	$	90,304
Large Cap Growth Fund		138,818
Mid Cap Growth Fund		11,740
Small-Mid Cap Growth Fund		875,561
Small-Mid Cap Value Fund		614
Small Cap Growth Fund		459,313
Small Cap Value Fund		38,601
Global Leaders Fund		18,686
International Leaders Fund		24,691
International Growth Fund		1,195,863
International Small Cap Growth Fund		7,703
Emerging Markets Leaders Fund		5,407
Emerging Markets Growth Fund		14,852
Emerging Markets Small Cap Growth Fund		12,911
Bond Fund		80,645
Income Fund		30,611
Low Duration Fund		1,942
Macro Allocation Fund		78,556


Name and Year of Birth	Position(s) Held with Trust	Term of Office⁽¹⁾ and Length of Time Served	Principal Occupation(s) During Past 5 Years	Number of Portfolios in Trust Complex Overseen by Trustee*	Other Directorships Held by Trustee**
Stephanie G. Braming, 1970⁽²⁾	Chairman of the Board and President, previously Senior Vice President	Chairman of the Board and President since 2018, and Senior Vice President 2014 to 2018	Global Head of Investment Management since 2017, portfolio manager (2014 to 2017) and Partner, William Blair	20	Chairman, William Blair SICAV

Arthur J. Simon, 1954⁽²⁾	Trustee	Since 2018	General Counsel and Partner, William Blair	20	Director, William Blair SICAV


Name and Year of Birth	Position(s) Held with Trust	Term of Office and Length of Time Served⁽¹⁾	Principal Occupation(s) During Past 5 Years
Marcelo Assalin, 1973	Senior Vice President	Since 2020	Associate, William Blair (since 2020); formerly, NN Investment Partners (2013-2020)

Michael P. Balkin, 1959	Senior Vice President	Since 2008	Partner, William Blair

Thomas Clarke, 1968	Senior Vice President	Since 2011	Partner, William Blair

Daniel Crowe, 1972	Senior Vice President	Since 2016	Partner, William Blair

Robert J. Duwa, 1967	Senior Vice President	Since 2019	Partner, William Blair


Trustee	Aggregate Compensation from the Funds		Pension or Retirement Benefits Accrued As Part of Trust Expenses		Estimated Annual Benefits Upon Retirement		Aggregate Compensation from the Trust⁽¹⁾
Vann A. Avedisian	$	156,000	$	0	$	0	$	156,000
Kathleen T. Barr	$	156,000	$	0	$	0	$	156,000
Daniel N. Leib	$	158,000	$	0	$	0	$	158,000
Dorri C. McWhorter⁽²⁾	$	136,000	$	0	$	0	$	136,000
Thomas J. Skelly	$	175,000	$	0	$	0	$	175,000
Steven R. Zenz	$	150,000	$	0	$	0	$	150,000

Total Trustee Compensation⁽³⁾	$	1,033,000	$	0	$	0	$	1,033,000