11. Share-Based Compensation

Our share-based compensation consists of stock options, restricted stock units (“RSU”), and performance stock units (“PSU”) and is used to compensate certain employees and non-employee directors. We also offer an employee stock purchase plan to eligible employees.

Most of our equity awards vest either annually on a pro rata basis, generally over a one- or three-year period or on a specific date if certain performance criteria are satisfied and certain equity values are attained. In addition, upon termination of service, all vested awards must be exercised generally within 90 days after termination, or these awards will be forfeited. The stock options have a 10-year contractual term and have an exercise price that is not less than the fair market value of the underlying common stock on the date of grant.

As of June 30, 2024, there were 12.7 million stock options, RSUs, and PSUs outstanding and 9.7 million shares available for grant under approved equity compensation plans.

Total share-based compensation expense was $40.8 million and $41.5 million for the three months ended June 30, 2024, and 2023, respectively, and $78.8 million and $81.7 million for the six months ended June 30, 2024, and 2023, respectively.

Performance-Based Stock Options

As of June 30, 2024, there is no unrecognized expense related to unvested performance-based stock option awards.

Performance Stock Units

In March 2024, we granted PSU awards under our Management Incentive Plan (“MIP”) for the incentive period of January 1, 2024 through December 31, 2024, and also as part of long-term incentive ("LTI") grants to certain members of management. These awards are primarily earned upon performance of key financial metrics and certain LTI awards are earned based upon our total shareholder return, a market condition, as compared to an indexed shareholder return over the course of a fiscal based three-year performance period, starting in the year of grant. The probability of vesting will continue to be evaluated throughout 2024, and share-based compensation will be recognized in accordance with that probability. Earned awards typically vest in the quarter following the conclusion of the performance period.

As of June 30, 2024, there was $46.9 million of share-based compensation expense related to unvested PSUs not yet recognized, which is expected to be recognized over a weighted average period of 2.2 years.

Restricted Stock Units

As of June 30, 2024, there was $188.0 million of share-based compensation expense related to unvested RSUs not yet recognized, which is expected to be recognized over a weighted average period of 1.8 years.

Term-Based Stock Options

As of June 30, 2024, there was $4.1 million of share-based compensation expense related to unvested term-based stock options not yet recognized, which is expected to be recognized over a weighted average period of 0.1 years.

Global Employee Stock Purchase Plan

A total of 1.3 million shares of common stock are available for future issuances under the plan as of June 30, 2024.