<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with Wdesk from Workiva, formerly WebFilings-->
<!-- -->
<linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <roleRef roleURI="http://www.onebeacon.com/role/AcqusitionsAndDispositions" xlink:href="ob-20140630.xsd#AcqusitionsAndDispositions" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/AcqusitionsAndDispositionsDetails" xlink:href="ob-20140630.xsd#AcqusitionsAndDispositionsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/CommonShareholdersEquity" xlink:href="ob-20140630.xsd#CommonShareholdersEquity" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/CommonShareholdersEquityDetails" xlink:href="ob-20140630.xsd#CommonShareholdersEquityDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ConsolidatedBalanceSheets" xlink:href="ob-20140630.xsd#ConsolidatedBalanceSheets" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:href="ob-20140630.xsd#ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ConsolidatedStatementsOfCashFlows" xlink:href="ob-20140630.xsd#ConsolidatedStatementsOfCashFlows" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ConsolidatedStatementsOfCommonShareholdersEquity" xlink:href="ob-20140630.xsd#ConsolidatedStatementsOfCommonShareholdersEquity" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ConsolidatedStatementsOfOperationsAndComprehensiveIncome" xlink:href="ob-20140630.xsd#ConsolidatedStatementsOfOperationsAndComprehensiveIncome" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ConsolidatingFinancialInformation" xlink:href="ob-20140630.xsd#ConsolidatingFinancialInformation" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ConsolidatingFinancialInformationConsolidatingBalanceSheetDetails" xlink:href="ob-20140630.xsd#ConsolidatingFinancialInformationConsolidatingBalanceSheetDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ConsolidatingFinancialInformationConsolidatingStatementOfCashFlowsDetails" xlink:href="ob-20140630.xsd#ConsolidatingFinancialInformationConsolidatingStatementOfCashFlowsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ConsolidatingFinancialInformationConsolidatingStatementOfOperationsAndComprehensiveLossDetails" xlink:href="ob-20140630.xsd#ConsolidatingFinancialInformationConsolidatingStatementOfOperationsAndComprehensiveLossDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ConsolidatingFinancialInformationTables" xlink:href="ob-20140630.xsd#ConsolidatingFinancialInformationTables" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/Debt" xlink:href="ob-20140630.xsd#Debt" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/DebtDetails" xlink:href="ob-20140630.xsd#DebtDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/DebtTables" xlink:href="ob-20140630.xsd#DebtTables" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/DiscontinuedOperations" xlink:href="ob-20140630.xsd#DiscontinuedOperations" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/DiscontinuedOperationsAdditionalDisclosuresDetails" xlink:href="ob-20140630.xsd#DiscontinuedOperationsAdditionalDisclosuresDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/DiscontinuedOperationsLossPerShareRelatedToDiscontinuedOperationsDetails" xlink:href="ob-20140630.xsd#DiscontinuedOperationsLossPerShareRelatedToDiscontinuedOperationsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/DiscontinuedOperationsSummaryOfReclassifiedBalancesAndRelatedItemsDetails" xlink:href="ob-20140630.xsd#DiscontinuedOperationsSummaryOfReclassifiedBalancesAndRelatedItemsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/DiscontinuedOperationsSummaryOfResultsOfOperationsDetails" xlink:href="ob-20140630.xsd#DiscontinuedOperationsSummaryOfResultsOfOperationsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/DiscontinuedOperationsTables" xlink:href="ob-20140630.xsd#DiscontinuedOperationsTables" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/DocumentAndEntityInformation" xlink:href="ob-20140630.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/EarningsPerShare" xlink:href="ob-20140630.xsd#EarningsPerShare" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/EarningsPerShareDetails" xlink:href="ob-20140630.xsd#EarningsPerShareDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/EarningsPerShareTables" xlink:href="ob-20140630.xsd#EarningsPerShareTables" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/EmployeeShareBasedIncentiveCompensationPlans" xlink:href="ob-20140630.xsd#EmployeeShareBasedIncentiveCompensationPlans" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/EmployeeShareBasedIncentiveCompensationPlansEmployeeShareBasedCompensationPlansDetails" xlink:href="ob-20140630.xsd#EmployeeShareBasedIncentiveCompensationPlansEmployeeShareBasedCompensationPlansDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/EmployeeShareBasedIncentiveCompensationPlansPerformanceSharesDetails" xlink:href="ob-20140630.xsd#EmployeeShareBasedIncentiveCompensationPlansPerformanceSharesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/EmployeeShareBasedIncentiveCompensationPlansRestrictedDetails" xlink:href="ob-20140630.xsd#EmployeeShareBasedIncentiveCompensationPlansRestrictedDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/EmployeeShareBasedIncentiveCompensationPlansTables" xlink:href="ob-20140630.xsd#EmployeeShareBasedIncentiveCompensationPlansTables" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/FairValueOfFinancialInstruments" xlink:href="ob-20140630.xsd#FairValueOfFinancialInstruments" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/FairValueOfFinancialInstrumentsDetails" xlink:href="ob-20140630.xsd#FairValueOfFinancialInstrumentsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/IncomeTaxes" xlink:href="ob-20140630.xsd#IncomeTaxes" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/IncomeTaxesDetails" xlink:href="ob-20140630.xsd#IncomeTaxesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecurities" xlink:href="ob-20140630.xsd#InvestmentSecurities" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesAssetBackedSecuritiesDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesAssetBackedSecuritiesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesChangeInNetUnrealizedGainsOrLossesForLevel3AssetsDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesChangeInNetUnrealizedGainsOrLossesForLevel3AssetsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesChangesInFairValueDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesChangesInFairValueDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesConvertibleFixedMaturityInvestmentsAndOtherInvestmentsDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesConvertibleFixedMaturityInvestmentsAndOtherInvestmentsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesCorporateDebtSecuritesDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesCorporateDebtSecuritesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesFairValueMeasurementsDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesFairValueMeasurementsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesFairValueRollforwardDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesFairValueRollforwardDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesFixedMaturityInvestmentGainsAndLossesDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesFixedMaturityInvestmentGainsAndLossesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesNetInvestmentIncomeDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesNetInvestmentIncomeDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesNetRealizedInvestmentGainsLossesDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesNetRealizedInvestmentGainsLossesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesNetUnrealizedInvestmentGainsAndLossesDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesNetUnrealizedInvestmentGainsAndLossesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesNonAgencySecuritiesDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesNonAgencySecuritiesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesOtherInvestmentsDetails" xlink:href="ob-20140630.xsd#InvestmentSecuritiesOtherInvestmentsDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesSecuritiesClassifiedAsLevel3Details" xlink:href="ob-20140630.xsd#InvestmentSecuritiesSecuritiesClassifiedAsLevel3Details" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/InvestmentSecuritiesTables" xlink:href="ob-20140630.xsd#InvestmentSecuritiesTables" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/LegalContingencies" xlink:href="ob-20140630.xsd#LegalContingencies" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/LegalContingenciesDetails" xlink:href="ob-20140630.xsd#LegalContingenciesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/NatureOfOperationsAndSummaryOfSignificantAccountingPolicies" xlink:href="ob-20140630.xsd#NatureOfOperationsAndSummaryOfSignificantAccountingPolicies" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesDetails" xlink:href="ob-20140630.xsd#NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:href="ob-20140630.xsd#NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/Reinsurance" xlink:href="ob-20140630.xsd#Reinsurance" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ReinsuranceDetails" xlink:href="ob-20140630.xsd#ReinsuranceDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/ReinsuranceTables" xlink:href="ob-20140630.xsd#ReinsuranceTables" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/RetirementPlans" xlink:href="ob-20140630.xsd#RetirementPlans" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/RetirementPlansPeriodicBenefitCostDetails" xlink:href="ob-20140630.xsd#RetirementPlansPeriodicBenefitCostDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/RetirementPlansTables" xlink:href="ob-20140630.xsd#RetirementPlansTables" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/SegmentInformation" xlink:href="ob-20140630.xsd#SegmentInformation" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/SegmentInformationDetails" xlink:href="ob-20140630.xsd#SegmentInformationDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/SegmentInformationTables" xlink:href="ob-20140630.xsd#SegmentInformationTables" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/UnpaidLossAndLossAdjustmentExpenseLaeReserves" xlink:href="ob-20140630.xsd#UnpaidLossAndLossAdjustmentExpenseLaeReserves" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/UnpaidLossAndLossAdjustmentExpenseLaeReservesDetails" xlink:href="ob-20140630.xsd#UnpaidLossAndLossAdjustmentExpenseLaeReservesDetails" xlink:type="simple" />
  <roleRef roleURI="http://www.onebeacon.com/role/UnpaidLossAndLossAdjustmentExpenseLaeReservesTables" xlink:href="ob-20140630.xsd#UnpaidLossAndLossAdjustmentExpenseLaeReservesTables" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/AcqusitionsAndDispositions" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/AcqusitionsAndDispositionsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_F425950BFDA3D293159A6EA8673C700E" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_8B921C311F09734EFAC56EA8673C5326" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_F425950BFDA3D293159A6EA8673C700E" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_8B921C311F09734EFAC56EA8673C5326" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_5BFD24DA824A530CD6F16EBA5A440193" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_8B921C311F09734EFAC56EA8673C5326" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_5BFD24DA824A530CD6F16EBA5A440193" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_D5CFE4E9E4D4E4C32AB56EBA5A44E680_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_5BFD24DA824A530CD6F16EBA5A440193" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_D5CFE4E9E4D4E4C32AB56EBA5A44E680_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_D5CFE4E9E4D4E4C32AB56EBA5A44E680" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_5BFD24DA824A530CD6F16EBA5A440193" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_D5CFE4E9E4D4E4C32AB56EBA5A44E680" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDiscontinuedOperationsMember" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_AC3A294406AC80A498A26EBA5A6332B2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_D5CFE4E9E4D4E4C32AB56EBA5A44E680" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_AC3A294406AC80A498A26EBA5A6332B2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_E6BE2D04FFF7F8F7770E6EA8673C68D8" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_8B921C311F09734EFAC56EA8673C5326" xlink:to="loc_dei_LegalEntityAxis_E6BE2D04FFF7F8F7770E6EA8673C68D8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_9074494940A05AF91CF96EA8673C5449_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_E6BE2D04FFF7F8F7770E6EA8673C68D8" xlink:to="loc_dei_EntityDomain_9074494940A05AF91CF96EA8673C5449_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_9074494940A05AF91CF96EA8673C5449" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_E6BE2D04FFF7F8F7770E6EA8673C68D8" xlink:to="loc_dei_EntityDomain_9074494940A05AF91CF96EA8673C5449" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_EssentiaInsuranceCompanyMember" xlink:label="loc_ob_EssentiaInsuranceCompanyMember_47AA711D152E612A04BC6EA8673C25FF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_9074494940A05AF91CF96EA8673C5449" xlink:to="loc_ob_EssentiaInsuranceCompanyMember_47AA711D152E612A04BC6EA8673C25FF" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ChangeInSurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations" xlink:label="loc_ob_ChangeInSurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations_B551C3640AADE7ED07586EBA59E61AD1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_F425950BFDA3D293159A6EA8673C700E" xlink:to="loc_ob_ChangeInSurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations_B551C3640AADE7ED07586EBA59E61AD1" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations" xlink:label="loc_ob_SurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations_5EE0A750CEDBF2E805F56EBA5D506045" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_F425950BFDA3D293159A6EA8673C700E" xlink:to="loc_ob_SurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations_5EE0A750CEDBF2E805F56EBA5D506045" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_63E280E930CD1EB763926EA8673C9B15" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_F425950BFDA3D293159A6EA8673C700E" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_63E280E930CD1EB763926EA8673C9B15" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_9564E3FA22A7D5504CA96EA8673C3427" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_F425950BFDA3D293159A6EA8673C700E" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_9564E3FA22A7D5504CA96EA8673C3427" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PremiumsWrittenNet" xlink:label="loc_us-gaap_PremiumsWrittenNet_89B64159667C97F909AB6EA8673C9541" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_F425950BFDA3D293159A6EA8673C700E" xlink:to="loc_us-gaap_PremiumsWrittenNet_89B64159667C97F909AB6EA8673C9541" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PremiumsEarnedNet" xlink:label="loc_us-gaap_PremiumsEarnedNet_24DB52839F1758F0F3346EA8673C6C60" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_F425950BFDA3D293159A6EA8673C700E" xlink:to="loc_us-gaap_PremiumsEarnedNet_24DB52839F1758F0F3346EA8673C6C60" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/CommonShareholdersEquity" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/CommonShareholdersEquityDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityClassOfTreasuryStockLineItems" xlink:label="loc_us-gaap_EquityClassOfTreasuryStockLineItems_F42556F26169E24412496A75DFCBF7B3" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfTreasuryStockTable" xlink:label="loc_us-gaap_ClassOfTreasuryStockTable_28F493FF5EAF8E9D108D6A75DFCB8C5C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_F42556F26169E24412496A75DFCBF7B3" xlink:to="loc_us-gaap_ClassOfTreasuryStockTable_28F493FF5EAF8E9D108D6A75DFCB8C5C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_DF140BD286911562E9386A75DFCBF0C0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfTreasuryStockTable_28F493FF5EAF8E9D108D6A75DFCB8C5C" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_DF140BD286911562E9386A75DFCBF0C0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_0C9AC4B3210A63D254016A75DFCB6453_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_DF140BD286911562E9386A75DFCBF0C0" xlink:to="loc_us-gaap_EquityComponentDomain_0C9AC4B3210A63D254016A75DFCB6453_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_0C9AC4B3210A63D254016A75DFCB6453" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_DF140BD286911562E9386A75DFCBF0C0" xlink:to="loc_us-gaap_EquityComponentDomain_0C9AC4B3210A63D254016A75DFCB6453" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ParentMember" xlink:label="loc_us-gaap_ParentMember_2E631B8C527F5F2C37486A75DFCBD158" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0C9AC4B3210A63D254016A75DFCB6453" xlink:to="loc_us-gaap_ParentMember_2E631B8C527F5F2C37486A75DFCBD158" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_F249B32AECE92F43D9966A75DFCB238A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0C9AC4B3210A63D254016A75DFCB6453" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_F249B32AECE92F43D9966A75DFCB238A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_8AD842A80BB6CA6036A06A75DFCB73FC" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfTreasuryStockTable_28F493FF5EAF8E9D108D6A75DFCB8C5C" xlink:to="loc_us-gaap_StatementClassOfStockAxis_8AD842A80BB6CA6036A06A75DFCB73FC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_B0CC344F090CEDA92E0E6A75DFCB0D42_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_8AD842A80BB6CA6036A06A75DFCB73FC" xlink:to="loc_us-gaap_ClassOfStockDomain_B0CC344F090CEDA92E0E6A75DFCB0D42_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_B0CC344F090CEDA92E0E6A75DFCB0D42" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_8AD842A80BB6CA6036A06A75DFCB73FC" xlink:to="loc_us-gaap_ClassOfStockDomain_B0CC344F090CEDA92E0E6A75DFCB0D42" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_82E9736FD64881E95B1C6A75DFCB1613" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_B0CC344F090CEDA92E0E6A75DFCB0D42" xlink:to="loc_us-gaap_CommonClassAMember_82E9736FD64881E95B1C6A75DFCB1613" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_879D6529563631E5D45A6A75DFCB9284" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_B0CC344F090CEDA92E0E6A75DFCB0D42" xlink:to="loc_us-gaap_CommonStockMember_879D6529563631E5D45A6A75DFCB9284" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockRepurchaseProgramAuthorizedAmount" xlink:label="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount_36C339D9211C96B795DE6A75DFCB0F49" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_F42556F26169E24412496A75DFCBF7B3" xlink:to="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount_36C339D9211C96B795DE6A75DFCB0F49" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_F118766EACEDCAA238E86A75DFCB3B0A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_F42556F26169E24412496A75DFCBF7B3" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_F118766EACEDCAA238E86A75DFCB3B0A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DividendsCommonStockCash" xlink:label="loc_us-gaap_DividendsCommonStockCash_D559A1924F0351E1DF986A75DFCBCC61" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_F42556F26169E24412496A75DFCBF7B3" xlink:to="loc_us-gaap_DividendsCommonStockCash_D559A1924F0351E1DF986A75DFCBCC61" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockDividendsPerShareCashPaid" xlink:label="loc_us-gaap_CommonStockDividendsPerShareCashPaid_7FF340354536C1BB25BD6A75DFCBA19B" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_F42556F26169E24412496A75DFCBF7B3" xlink:to="loc_us-gaap_CommonStockDividendsPerShareCashPaid_7FF340354536C1BB25BD6A75DFCBA19B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax_A0C4E382FEFF36CDA9376A75DFCBA48D" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_F42556F26169E24412496A75DFCBF7B3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax_A0C4E382FEFF36CDA9376A75DFCBA48D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_3AD9E31D2107DEF5B32A6A75DFCBB7C1" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityClassOfTreasuryStockLineItems_F42556F26169E24412496A75DFCBF7B3" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_3AD9E31D2107DEF5B32A6A75DFCBB7C1" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/ConsolidatedBalanceSheets" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_61C86F0809C3066D310069FD0EE384EA" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_8929469EAAA254E5BE2769FD0EE24BC2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_61C86F0809C3066D310069FD0EE384EA" xlink:to="loc_us-gaap_StatementTable_8929469EAAA254E5BE2769FD0EE24BC2" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_B806455E01ECB780F5A869FD0EE2D4C6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8929469EAAA254E5BE2769FD0EE24BC2" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_B806455E01ECB780F5A869FD0EE2D4C6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_2EE57FAF5A550D90342569FD0EE28D20_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_B806455E01ECB780F5A869FD0EE2D4C6" xlink:to="loc_us-gaap_EquityComponentDomain_2EE57FAF5A550D90342569FD0EE28D20_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_2EE57FAF5A550D90342569FD0EE28D20" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_B806455E01ECB780F5A869FD0EE2D4C6" xlink:to="loc_us-gaap_EquityComponentDomain_2EE57FAF5A550D90342569FD0EE28D20" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember" xlink:label="loc_us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember_79FCA880E40D0AF61A7A69FD0EE3241F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2EE57FAF5A550D90342569FD0EE28D20" xlink:to="loc_us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember_79FCA880E40D0AF61A7A69FD0EE3241F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_023AECB25933026B470869FD0EE3C83D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2EE57FAF5A550D90342569FD0EE28D20" xlink:to="loc_us-gaap_RetainedEarningsMember_023AECB25933026B470869FD0EE3C83D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_17B88FB71A4C41B4DD4F69FD0EE3C903" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2EE57FAF5A550D90342569FD0EE28D20" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_17B88FB71A4C41B4DD4F69FD0EE3C903" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NoncontrollingInterestMember" xlink:label="loc_us-gaap_NoncontrollingInterestMember_AF94332A67BA522D30FF69FD0EE3CBE4" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2EE57FAF5A550D90342569FD0EE28D20" xlink:to="loc_us-gaap_NoncontrollingInterestMember_AF94332A67BA522D30FF69FD0EE3CBE4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_61C86F0809C3066D310069FD0EE384EA" xlink:to="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InvestmentsAbstract" xlink:label="loc_us-gaap_InvestmentsAbstract_A9AA3A2F70AE08D99A6069FD0EE37D24" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:to="loc_us-gaap_InvestmentsAbstract_A9AA3A2F70AE08D99A6069FD0EE37D24" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesDebt" xlink:label="loc_us-gaap_TradingSecuritiesDebt_08EEF055C3711C7B131B69FD0EE3792A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsAbstract_A9AA3A2F70AE08D99A6069FD0EE37D24" xlink:to="loc_us-gaap_TradingSecuritiesDebt_08EEF055C3711C7B131B69FD0EE3792A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShortTermInvestments" xlink:label="loc_us-gaap_ShortTermInvestments_4A786B5E5D8BE655282169FD0EE377FB" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsAbstract_A9AA3A2F70AE08D99A6069FD0EE37D24" xlink:to="loc_us-gaap_ShortTermInvestments_4A786B5E5D8BE655282169FD0EE377FB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesEquity" xlink:label="loc_us-gaap_TradingSecuritiesEquity_E7A235261086017BF86569FD0EE307CB" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsAbstract_A9AA3A2F70AE08D99A6069FD0EE37D24" xlink:to="loc_us-gaap_TradingSecuritiesEquity_E7A235261086017BF86569FD0EE307CB" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TradingSecuritiesConvertibleFixedMaturityInvestments" xlink:label="loc_ob_TradingSecuritiesConvertibleFixedMaturityInvestments_C20520DFE738FC2DA05F69FD0EE3867A" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsAbstract_A9AA3A2F70AE08D99A6069FD0EE37D24" xlink:to="loc_ob_TradingSecuritiesConvertibleFixedMaturityInvestments_C20520DFE738FC2DA05F69FD0EE3867A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherInvestments" xlink:label="loc_us-gaap_OtherInvestments_2848BF4A29A67A7751B569FD0EE3C728" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsAbstract_A9AA3A2F70AE08D99A6069FD0EE37D24" xlink:to="loc_us-gaap_OtherInvestments_2848BF4A29A67A7751B569FD0EE3C728" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Investments" xlink:label="loc_us-gaap_Investments_138B15A044AF59D326D469FD0EE45648" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsAbstract_A9AA3A2F70AE08D99A6069FD0EE37D24" xlink:to="loc_us-gaap_Investments_138B15A044AF59D326D469FD0EE45648" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_6E04649BC98D50AF616169FD0EE45EBA" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_6E04649BC98D50AF616169FD0EE45EBA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRecoverables" xlink:label="loc_us-gaap_ReinsuranceRecoverables_4EF82B28E3BF919FE88669FD0EE4AB03" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:to="loc_us-gaap_ReinsuranceRecoverables_4EF82B28E3BF919FE88669FD0EE4AB03" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PremiumsReceivableAtCarryingValue" xlink:label="loc_us-gaap_PremiumsReceivableAtCarryingValue_68DD357326F409278EEA69FD0EE42BEE" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:to="loc_us-gaap_PremiumsReceivableAtCarryingValue_68DD357326F409278EEA69FD0EE42BEE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredPolicyAcquisitionCosts" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCosts_49E59C42358E4DD7EEAF69FD0EE47A50" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:to="loc_us-gaap_DeferredPolicyAcquisitionCosts_49E59C42358E4DD7EEAF69FD0EE47A50" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsLiabilitiesNet" xlink:label="loc_us-gaap_DeferredTaxAssetsLiabilitiesNet_74DF678BFD600E4610F569FD0EE42C38" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:to="loc_us-gaap_DeferredTaxAssetsLiabilitiesNet_74DF678BFD600E4610F569FD0EE42C38" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccruedInvestmentIncomeReceivable" xlink:label="loc_us-gaap_AccruedInvestmentIncomeReceivable_D072B92977FBDAD8E7CD69FD0EE496B0" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:to="loc_us-gaap_AccruedInvestmentIncomeReceivable_D072B92977FBDAD8E7CD69FD0EE496B0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReceivablesFromBrokersDealersAndClearingOrganizations" xlink:label="loc_us-gaap_ReceivablesFromBrokersDealersAndClearingOrganizations_789E33386FB93BD63F0769FD0EE46ACB" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:to="loc_us-gaap_ReceivablesFromBrokersDealersAndClearingOrganizations_789E33386FB93BD63F0769FD0EE46ACB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherAssets" xlink:label="loc_us-gaap_OtherAssets_26BE647A60035198EE1D69FD0EE458B6" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:to="loc_us-gaap_OtherAssets_26BE647A60035198EE1D69FD0EE458B6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsHeldForSaleAtCarryingValue" xlink:label="loc_us-gaap_AssetsHeldForSaleAtCarryingValue_0ED8727E8A70B44C8F5369FD0EE4CF60" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:to="loc_us-gaap_AssetsHeldForSaleAtCarryingValue_0ED8727E8A70B44C8F5369FD0EE4CF60" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_6042604C5F497809E93F69FD0EE4F1F7" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_184011680D16D792D1EF69FD0EE32860" xlink:to="loc_us-gaap_Assets_6042604C5F497809E93F69FD0EE4F1F7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesAbstract" xlink:label="loc_us-gaap_LiabilitiesAbstract_DC474A338EFF0D95991F69FD0EE462D5" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_61C86F0809C3066D310069FD0EE384EA" xlink:to="loc_us-gaap_LiabilitiesAbstract_DC474A338EFF0D95991F69FD0EE462D5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_B9C31098089B1771E0F869FD0EE4A841" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_DC474A338EFF0D95991F69FD0EE462D5" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_B9C31098089B1771E0F869FD0EE4A841" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_UnearnedPremiums" xlink:label="loc_us-gaap_UnearnedPremiums_6F0A90BCA1C6EBC411A369FD0EE43DFF" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_DC474A338EFF0D95991F69FD0EE462D5" xlink:to="loc_us-gaap_UnearnedPremiums_6F0A90BCA1C6EBC411A369FD0EE43DFF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaap_LongTermDebt_12E9EB6F2B62DA98373D69FD0EE47AEF" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_DC474A338EFF0D95991F69FD0EE462D5" xlink:to="loc_us-gaap_LongTermDebt_12E9EB6F2B62DA98373D69FD0EE47AEF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PayablesToBrokerDealersAndClearingOrganizations" xlink:label="loc_us-gaap_PayablesToBrokerDealersAndClearingOrganizations_77AED63B371BF101735869FD0EE55C6D" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_DC474A338EFF0D95991F69FD0EE462D5" xlink:to="loc_us-gaap_PayablesToBrokerDealersAndClearingOrganizations_77AED63B371BF101735869FD0EE55C6D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLiabilities" xlink:label="loc_us-gaap_OtherLiabilities_D59F556B14A6670A1C6F69FD0EE5494F" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_DC474A338EFF0D95991F69FD0EE462D5" xlink:to="loc_us-gaap_OtherLiabilities_D59F556B14A6670A1C6F69FD0EE5494F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesOfAssetsHeldForSale" xlink:label="loc_us-gaap_LiabilitiesOfAssetsHeldForSale_1272AA764C27A0572A3269FD0EE5E1B4" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_DC474A338EFF0D95991F69FD0EE462D5" xlink:to="loc_us-gaap_LiabilitiesOfAssetsHeldForSale_1272AA764C27A0572A3269FD0EE5E1B4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaap_Liabilities_7D29AEEC4E24DB44C7F269FD0EE5AC1A" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_DC474A338EFF0D95991F69FD0EE462D5" xlink:to="loc_us-gaap_Liabilities_7D29AEEC4E24DB44C7F269FD0EE5AC1A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_BB8E126C865F54CD829D69FD0EE50A19" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_61C86F0809C3066D310069FD0EE384EA" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_BB8E126C865F54CD829D69FD0EE50A19" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="loc_us-gaap_StockholdersEquityAbstract_9D274560E6A8B9516F5569FD0EE5F9FF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_BB8E126C865F54CD829D69FD0EE50A19" xlink:to="loc_us-gaap_StockholdersEquityAbstract_9D274560E6A8B9516F5569FD0EE5F9FF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStocksIncludingAdditionalPaidInCapital" xlink:label="loc_us-gaap_CommonStocksIncludingAdditionalPaidInCapital_B6423B3D51138604E9E669FD0EE574EE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9D274560E6A8B9516F5569FD0EE5F9FF" xlink:to="loc_us-gaap_CommonStocksIncludingAdditionalPaidInCapital_B6423B3D51138604E9E669FD0EE574EE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_549446674D75C1AA371769FD0EE56146" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9D274560E6A8B9516F5569FD0EE5F9FF" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_549446674D75C1AA371769FD0EE56146" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_1E7504777B1101E3A0C969FD0EE551A3" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9D274560E6A8B9516F5569FD0EE5F9FF" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_1E7504777B1101E3A0C969FD0EE551A3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_329A87FDD3DBCAFFEB2869FD0EE5B91D" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9D274560E6A8B9516F5569FD0EE5F9FF" xlink:to="loc_us-gaap_StockholdersEquity_329A87FDD3DBCAFFEB2869FD0EE5B91D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinorityInterest" xlink:label="loc_us-gaap_MinorityInterest_FC58FA0E1802108A8EE169FD0EE52D4D" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9D274560E6A8B9516F5569FD0EE5F9FF" xlink:to="loc_us-gaap_MinorityInterest_FC58FA0E1802108A8EE169FD0EE52D4D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_F7A81D5B102BA52F6A8669FD0EE51D6A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAbstract_BB8E126C865F54CD829D69FD0EE50A19" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_F7A81D5B102BA52F6A8669FD0EE51D6A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_D575F23A1456164B845169FD0EE59C26" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_61C86F0809C3066D310069FD0EE384EA" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_D575F23A1456164B845169FD0EE59C26" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/ConsolidatedStatementsOfCashFlows" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_A53AC37E74EAEA362B2669FD0EC2D8DB" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_67FE05E967A2441FD47769FD0EC26F8C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_A53AC37E74EAEA362B2669FD0EC2D8DB" xlink:to="loc_us-gaap_StatementTable_67FE05E967A2441FD47769FD0EC26F8C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_611F99D3B78F984D997F69FD0EC26982" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_67FE05E967A2441FD47769FD0EC26F8C" xlink:to="loc_us-gaap_StatementScenarioAxis_611F99D3B78F984D997F69FD0EC26982" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_166652EFE48D1A9F1E2969FD0EC2B48E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_611F99D3B78F984D997F69FD0EC26982" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_166652EFE48D1A9F1E2969FD0EC2B48E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_166652EFE48D1A9F1E2969FD0EC2B48E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_611F99D3B78F984D997F69FD0EC26982" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_166652EFE48D1A9F1E2969FD0EC2B48E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_D2CEA06B5FEBAD45318069FD0EC2834D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_A53AC37E74EAEA362B2669FD0EC2D8DB" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_D2CEA06B5FEBAD45318069FD0EC2834D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_9AFFE3F807616785B7C269FD0EC2427A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_D2CEA06B5FEBAD45318069FD0EC2834D" xlink:to="loc_us-gaap_ProfitLoss_9AFFE3F807616785B7C269FD0EC2427A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_6142EFBAB8994FCDD31969FD0EC3D5B1" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_D2CEA06B5FEBAD45318069FD0EC2834D" xlink:to="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_6142EFBAB8994FCDD31969FD0EC3D5B1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_77AA42EBC9BEBCD6447169FD0EC327DC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_6142EFBAB8994FCDD31969FD0EC3D5B1" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_77AA42EBC9BEBCD6447169FD0EC327DC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_A042F004D93387A980D769FD0EC35370" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_6142EFBAB8994FCDD31969FD0EC3D5B1" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_A042F004D93387A980D769FD0EC35370" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GainLossOnInvestments" xlink:label="loc_us-gaap_GainLossOnInvestments_4A363E94AADFAAA0604C69FD0EC3E2DE" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_6142EFBAB8994FCDD31969FD0EC3D5B1" xlink:to="loc_us-gaap_GainLossOnInvestments_4A363E94AADFAAA0604C69FD0EC3E2DE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_832A1CD88CEF5CA321DC69FD0EC3DE8C" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_6142EFBAB8994FCDD31969FD0EC3D5B1" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_832A1CD88CEF5CA321DC69FD0EC3DE8C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_CAF02D4D409FD9E8EF3969FD0EC3C651" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_6142EFBAB8994FCDD31969FD0EC3D5B1" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_CAF02D4D409FD9E8EF3969FD0EC3C651" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_ACBED9B742E0A8F2D1EC69FD0EC303EA" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_D2CEA06B5FEBAD45318069FD0EC2834D" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_ACBED9B742E0A8F2D1EC69FD0EC303EA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInLossAndLossAdjustmentExpenseReserve" xlink:label="loc_us-gaap_IncreaseDecreaseInLossAndLossAdjustmentExpenseReserve_0504D60090EA5A3E476669FD0EC3FECD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_ACBED9B742E0A8F2D1EC69FD0EC303EA" xlink:to="loc_us-gaap_IncreaseDecreaseInLossAndLossAdjustmentExpenseReserve_0504D60090EA5A3E476669FD0EC3FECD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInUnearnedPremiums" xlink:label="loc_us-gaap_IncreaseDecreaseInUnearnedPremiums_8A3FFBBC11908905896169FD0EC3864E" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_ACBED9B742E0A8F2D1EC69FD0EC303EA" xlink:to="loc_us-gaap_IncreaseDecreaseInUnearnedPremiums_8A3FFBBC11908905896169FD0EC3864E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInPremiumsReceivable" xlink:label="loc_us-gaap_IncreaseDecreaseInPremiumsReceivable_5A791A5CD41A6F5E0B7C69FD0EC37FB3" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_ACBED9B742E0A8F2D1EC69FD0EC303EA" xlink:to="loc_us-gaap_IncreaseDecreaseInPremiumsReceivable_5A791A5CD41A6F5E0B7C69FD0EC37FB3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInReinsuranceRecoverable" xlink:label="loc_us-gaap_IncreaseDecreaseInReinsuranceRecoverable_1D67382F51E18662327069FD0EC30952" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_ACBED9B742E0A8F2D1EC69FD0EC303EA" xlink:to="loc_us-gaap_IncreaseDecreaseInReinsuranceRecoverable_1D67382F51E18662327069FD0EC30952" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_F180EE8984DEDE92030769FD0EC31A7C" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_ACBED9B742E0A8F2D1EC69FD0EC303EA" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_F180EE8984DEDE92030769FD0EC31A7C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_3E56D5AAB1B26008563269FD0EC4EAF8" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_ACBED9B742E0A8F2D1EC69FD0EC303EA" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_3E56D5AAB1B26008563269FD0EC4EAF8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations" xlink:label="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_CC94575F47223D7243BD69FD0EC4833C" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_D2CEA06B5FEBAD45318069FD0EC2834D" xlink:to="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_CC94575F47223D7243BD69FD0EC4833C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_2A7331AEFFEDDC7908B069FD0EC42A8D" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_D2CEA06B5FEBAD45318069FD0EC2834D" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_2A7331AEFFEDDC7908B069FD0EC42A8D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_A53AC37E74EAEA362B2669FD0EC2D8DB" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsForProceedsFromShortTermInvestments" xlink:label="loc_us-gaap_PaymentsForProceedsFromShortTermInvestments_9FFBF06CFC8366EDCA3769FD0EC4D75B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_us-gaap_PaymentsForProceedsFromShortTermInvestments_9FFBF06CFC8366EDCA3769FD0EC4D75B" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ProceedsFromMaturitiesOfTradingSecuritiesDebt" xlink:label="loc_ob_ProceedsFromMaturitiesOfTradingSecuritiesDebt_F4BE0711A6105182525F69FD0EC43351" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_ob_ProceedsFromMaturitiesOfTradingSecuritiesDebt_F4BE0711A6105182525F69FD0EC43351" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ProceedsFromSaleOfTradingSecuritiesDebt" xlink:label="loc_ob_ProceedsFromSaleOfTradingSecuritiesDebt_5C4C3998CF125EE94CFF69FD0EC4CA78" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_ob_ProceedsFromSaleOfTradingSecuritiesDebt_5C4C3998CF125EE94CFF69FD0EC4CA78" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ProceedsFromSaleOfTradingCommonEquitySecurities" xlink:label="loc_ob_ProceedsFromSaleOfTradingCommonEquitySecurities_E6AB6C9CF267D538596369FD0EC470D1" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_ob_ProceedsFromSaleOfTradingCommonEquitySecurities_E6AB6C9CF267D538596369FD0EC470D1" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ProceedsFromSaleOfTradingSecuritiesConvertibleFixedMaturityInvestments" xlink:label="loc_ob_ProceedsFromSaleOfTradingSecuritiesConvertibleFixedMaturityInvestments_3156F20C7111BAFCDFA169FD0EC4BB51" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_ob_ProceedsFromSaleOfTradingSecuritiesConvertibleFixedMaturityInvestments_3156F20C7111BAFCDFA169FD0EC4BB51" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments" xlink:label="loc_us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments_C43449C16BB0186C8C6B69FD0EC46AB8" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments_C43449C16BB0186C8C6B69FD0EC46AB8" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PaymentsToAcquireTradingSecuritiesDebt" xlink:label="loc_ob_PaymentsToAcquireTradingSecuritiesDebt_D19C2D95742450364BDA69FD0EC4D8DE" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_ob_PaymentsToAcquireTradingSecuritiesDebt_D19C2D95742450364BDA69FD0EC4D8DE" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PaymentsToAcquireTradingCommonEquitySecurities" xlink:label="loc_ob_PaymentsToAcquireTradingCommonEquitySecurities_EB566DE0C70D2D474DC569FD0EC56EAA" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_ob_PaymentsToAcquireTradingCommonEquitySecurities_EB566DE0C70D2D474DC569FD0EC56EAA" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PaymentsToAcquireTradingSecuritiesConvertibleFixedMaturityInvestments" xlink:label="loc_ob_PaymentsToAcquireTradingSecuritiesConvertibleFixedMaturityInvestments_78C57C553E2F33DD746869FD0EC5BD0F" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_ob_PaymentsToAcquireTradingSecuritiesConvertibleFixedMaturityInvestments_78C57C553E2F33DD746869FD0EC5BD0F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireOtherInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireOtherInvestments_997989C691394E842D6F69FD0EC51407" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_us-gaap_PaymentsToAcquireOtherInvestments_997989C691394E842D6F69FD0EC51407" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_F893C69CB3C6872A5F6C69FD0EC5A194" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_F893C69CB3C6872A5F6C69FD0EC5A194" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_IncreaseDecreaseInUnsettledAccountsReceivableAndAccountsPayable" xlink:label="loc_ob_IncreaseDecreaseInUnsettledAccountsReceivableAndAccountsPayable_7433F5E38444073E086969FD0EC59676" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_ob_IncreaseDecreaseInUnsettledAccountsReceivableAndAccountsPayable_7433F5E38444073E086969FD0EC59676" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_FD90D01327ECFC8BF86E69FD0EC58080" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_FD90D01327ECFC8BF86E69FD0EC58080" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations_9E6CD255D33C455A500C69FD0EC58195" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations_9E6CD255D33C455A500C69FD0EC58195" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations" xlink:label="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_A297719180AA467D771369FD0EC5FE9E" xlink:type="locator" />
    <definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_A297719180AA467D771369FD0EC5FE9E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_ABD5389C80948ED5640369FD0EC5CA52" xlink:type="locator" />
    <definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_90B16242AC43ADC85F5F69FD0EC4AE2A" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_ABD5389C80948ED5640369FD0EC5CA52" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_FB6E89A8F49ECB728D5469FD0EC577EC" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_A53AC37E74EAEA362B2669FD0EC2D8DB" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_FB6E89A8F49ECB728D5469FD0EC577EC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsOfDividendsCommonStock" xlink:label="loc_us-gaap_PaymentsOfDividendsCommonStock_395388DF036B388660A969FD0EC50696" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_FB6E89A8F49ECB728D5469FD0EC577EC" xlink:to="loc_us-gaap_PaymentsOfDividendsCommonStock_395388DF036B388660A969FD0EC50696" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ProceedsFromSaleOfSubsidiary" xlink:label="loc_ob_ProceedsFromSaleOfSubsidiary_93364BC1E0F91A8582AB69FD0EC68764" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_FB6E89A8F49ECB728D5469FD0EC577EC" xlink:to="loc_ob_ProceedsFromSaleOfSubsidiary_93364BC1E0F91A8582AB69FD0EC68764" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:label="loc_us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_7BF3B5692301D91EC54E69FD0EC66FEE" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_FB6E89A8F49ECB728D5469FD0EC577EC" xlink:to="loc_us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_7BF3B5692301D91EC54E69FD0EC66FEE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations_BE7B8B13ED32F5125A4D69FD0EC6856A" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_FB6E89A8F49ECB728D5469FD0EC577EC" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations_BE7B8B13ED32F5125A4D69FD0EC6856A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashProvidedByUsedInFinancingActivitiesDiscontinuedOperations" xlink:label="loc_us-gaap_CashProvidedByUsedInFinancingActivitiesDiscontinuedOperations_F819CA006D0A270CB1A569FD0EC63DD3" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_FB6E89A8F49ECB728D5469FD0EC577EC" xlink:to="loc_us-gaap_CashProvidedByUsedInFinancingActivitiesDiscontinuedOperations_F819CA006D0A270CB1A569FD0EC63DD3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_70B5D428EC01964AE1CB69FD0EC6DA3D" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_FB6E89A8F49ECB728D5469FD0EC577EC" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_70B5D428EC01964AE1CB69FD0EC6DA3D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_739D8025DE19724DF9C169FD0EC6163D" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_FB6E89A8F49ECB728D5469FD0EC577EC" xlink:to="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_739D8025DE19724DF9C169FD0EC6163D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_24A93641098A5EFE4E4069FD0EC6B594" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_A53AC37E74EAEA362B2669FD0EC2D8DB" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_24A93641098A5EFE4E4069FD0EC6B594" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/ConsolidatedStatementsOfCommonShareholdersEquity" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_A6A0FA8E44412DE4595D7E0EC6D1DAA1" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_9BEF5B243490D8A4DF787E0EC6CF8A58" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_A6A0FA8E44412DE4595D7E0EC6D1DAA1" xlink:to="loc_us-gaap_StatementTable_9BEF5B243490D8A4DF787E0EC6CF8A58" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_18A7B05A6D6B7FF707877E0EC6CF62A6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_9BEF5B243490D8A4DF787E0EC6CF8A58" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_18A7B05A6D6B7FF707877E0EC6CF62A6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_D0F3A20DF8CA1A3E3A4A7E0EC6CF275D_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_18A7B05A6D6B7FF707877E0EC6CF62A6" xlink:to="loc_us-gaap_EquityComponentDomain_D0F3A20DF8CA1A3E3A4A7E0EC6CF275D_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_D0F3A20DF8CA1A3E3A4A7E0EC6CF275D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_18A7B05A6D6B7FF707877E0EC6CF62A6" xlink:to="loc_us-gaap_EquityComponentDomain_D0F3A20DF8CA1A3E3A4A7E0EC6CF275D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember" xlink:label="loc_us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember_6A4C69790EAB026B40937E0EC6CFBFD2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_D0F3A20DF8CA1A3E3A4A7E0EC6CF275D" xlink:to="loc_us-gaap_CommonStockIncludingAdditionalPaidInCapitalMember_6A4C69790EAB026B40937E0EC6CFBFD2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="loc_us-gaap_RetainedEarningsMember_1BFA0596B38FDD6AE66D7E0EC6CF751A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_D0F3A20DF8CA1A3E3A4A7E0EC6CF275D" xlink:to="loc_us-gaap_RetainedEarningsMember_1BFA0596B38FDD6AE66D7E0EC6CF751A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_87CC133E72CDB4A20C5D7E0EC6D0220A" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_D0F3A20DF8CA1A3E3A4A7E0EC6CF275D" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_87CC133E72CDB4A20C5D7E0EC6D0220A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ParentMember" xlink:label="loc_us-gaap_ParentMember_343F7534837108E85CE67E0EC6D0C3CB" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_D0F3A20DF8CA1A3E3A4A7E0EC6CF275D" xlink:to="loc_us-gaap_ParentMember_343F7534837108E85CE67E0EC6D0C3CB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NoncontrollingInterestMember" xlink:label="loc_us-gaap_NoncontrollingInterestMember_639F27ACD9AEF542454A7E0EC6D11F6A" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_D0F3A20DF8CA1A3E3A4A7E0EC6CF275D" xlink:to="loc_us-gaap_NoncontrollingInterestMember_639F27ACD9AEF542454A7E0EC6D11F6A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_EBC2E2F7695021AD09C47E0EC6D19F81" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_A6A0FA8E44412DE4595D7E0EC6D1DAA1" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_EBC2E2F7695021AD09C47E0EC6D19F81" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_1C4E9F80E4B0E65A6FFE7E0EC6D18912" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_EBC2E2F7695021AD09C47E0EC6D19F81" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_1C4E9F80E4B0E65A6FFE7E0EC6D18912" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_28D684FF43AC6BA26A357E0EC6D1222D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_EBC2E2F7695021AD09C47E0EC6D19F81" xlink:to="loc_us-gaap_ProfitLoss_28D684FF43AC6BA26A357E0EC6D1222D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_07EAD1A3D709539ACCDE7E0EC6D1FA01" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_EBC2E2F7695021AD09C47E0EC6D19F81" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_07EAD1A3D709539ACCDE7E0EC6D1FA01" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_BC27D45D271BB4B1E1D67E0EC6D248B5" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_EBC2E2F7695021AD09C47E0EC6D19F81" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_BC27D45D271BB4B1E1D67E0EC6D248B5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_D2ACC0CE9E28794989737E0EC6D28EAB" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_EBC2E2F7695021AD09C47E0EC6D19F81" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_D2ACC0CE9E28794989737E0EC6D28EAB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_4538E72124242410AC317E0EC6D20238" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_EBC2E2F7695021AD09C47E0EC6D19F81" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_4538E72124242410AC317E0EC6D20238" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_6289540200F0D60BF4827E0EC6D296F7" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_EBC2E2F7695021AD09C47E0EC6D19F81" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_6289540200F0D60BF4827E0EC6D296F7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DividendsCommonStockCash" xlink:label="loc_us-gaap_DividendsCommonStockCash_12B91457A648909C7DE47E0EC6D26C62" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_EBC2E2F7695021AD09C47E0EC6D19F81" xlink:to="loc_us-gaap_DividendsCommonStockCash_12B91457A648909C7DE47E0EC6D26C62" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/ConsolidatedStatementsOfOperationsAndComprehensiveIncome" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_F72B7358081AA2AF8EBA69FD0ED365E2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_StatementTable_F72B7358081AA2AF8EBA69FD0ED365E2" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_6E037D7C3E91865F12A869FD0ED3038D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_F72B7358081AA2AF8EBA69FD0ED365E2" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_6E037D7C3E91865F12A869FD0ED3038D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_6BB20D8B07D39502846E69FD0ED3EFB0_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_6E037D7C3E91865F12A869FD0ED3038D" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_6BB20D8B07D39502846E69FD0ED3EFB0_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_6BB20D8B07D39502846E69FD0ED3EFB0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_6E037D7C3E91865F12A869FD0ED3038D" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_6BB20D8B07D39502846E69FD0ED3EFB0" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RunoffMember" xlink:label="loc_ob_RunoffMember_F72A15552282109DB04369FD0ED3762E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_6BB20D8B07D39502846E69FD0ED3EFB0" xlink:to="loc_ob_RunoffMember_F72A15552282109DB04369FD0ED3762E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_8635CAD38E03C4B9701869FD0ED3FBA0" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_F72B7358081AA2AF8EBA69FD0ED365E2" xlink:to="loc_us-gaap_StatementScenarioAxis_8635CAD38E03C4B9701869FD0ED3FBA0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_75EC96EF705A0684585869FD0ED4AC45_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_8635CAD38E03C4B9701869FD0ED3FBA0" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_75EC96EF705A0684585869FD0ED4AC45_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_75EC96EF705A0684585869FD0ED4AC45" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_8635CAD38E03C4B9701869FD0ED3FBA0" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_75EC96EF705A0684585869FD0ED4AC45" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RevenuesAbstract" xlink:label="loc_us-gaap_RevenuesAbstract_103169737814E4BDDDFC69FD0ED4C45A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_RevenuesAbstract_103169737814E4BDDDFC69FD0ED4C45A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PremiumsEarnedNet" xlink:label="loc_us-gaap_PremiumsEarnedNet_02C3C4B2E7DDFB47F62769FD0ED4AA1B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_103169737814E4BDDDFC69FD0ED4C45A" xlink:to="loc_us-gaap_PremiumsEarnedNet_02C3C4B2E7DDFB47F62769FD0ED4AA1B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetInvestmentIncome" xlink:label="loc_us-gaap_NetInvestmentIncome_02C4E923EFF7746F77D469FD0ED4ECEE" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_103169737814E4BDDDFC69FD0ED4C45A" xlink:to="loc_us-gaap_NetInvestmentIncome_02C4E923EFF7746F77D469FD0ED4ECEE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GainLossOnInvestments" xlink:label="loc_us-gaap_GainLossOnInvestments_D83745B22FF89269B5D069FD0ED47341" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_103169737814E4BDDDFC69FD0ED4C45A" xlink:to="loc_us-gaap_GainLossOnInvestments_D83745B22FF89269B5D069FD0ED47341" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_41F00A8EC41E83C1A2BA69FD0ED4C554" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_103169737814E4BDDDFC69FD0ED4C45A" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_41F00A8EC41E83C1A2BA69FD0ED4C554" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_75A953CDD5B239E2AFFA69FD0ED470F6" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_103169737814E4BDDDFC69FD0ED4C45A" xlink:to="loc_us-gaap_Revenues_75A953CDD5B239E2AFFA69FD0ED470F6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BenefitsLossesAndExpensesAbstract" xlink:label="loc_us-gaap_BenefitsLossesAndExpensesAbstract_A7AE10D795952678153969FD0ED45E14" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_BenefitsLossesAndExpensesAbstract_A7AE10D795952678153969FD0ED45E14" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PolicyholderBenefitsAndClaimsIncurredNet" xlink:label="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_94E4E8DDBABC185F209069FD0ED4E897" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BenefitsLossesAndExpensesAbstract_A7AE10D795952678153969FD0ED45E14" xlink:to="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_94E4E8DDBABC185F209069FD0ED4E897" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InsuranceAndReinsuranceAcquisitionExpenses" xlink:label="loc_ob_InsuranceAndReinsuranceAcquisitionExpenses_A3A4154A0EDF25BA093B69FD0ED4E532" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BenefitsLossesAndExpensesAbstract_A7AE10D795952678153969FD0ED45E14" xlink:to="loc_ob_InsuranceAndReinsuranceAcquisitionExpenses_A3A4154A0EDF25BA093B69FD0ED4E532" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherUnderwritingExpense" xlink:label="loc_us-gaap_OtherUnderwritingExpense_6734E6B09D9106163CF269FD0ED4DC28" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BenefitsLossesAndExpensesAbstract_A7AE10D795952678153969FD0ED45E14" xlink:to="loc_us-gaap_OtherUnderwritingExpense_6734E6B09D9106163CF269FD0ED4DC28" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_0FC6AA558766A3CB15CC69FD0ED4C6A8" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BenefitsLossesAndExpensesAbstract_A7AE10D795952678153969FD0ED45E14" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_0FC6AA558766A3CB15CC69FD0ED4C6A8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestExpenseDebt" xlink:label="loc_us-gaap_InterestExpenseDebt_F9258C0C7A5F4F08DADE69FD0ED53CC3" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BenefitsLossesAndExpensesAbstract_A7AE10D795952678153969FD0ED45E14" xlink:to="loc_us-gaap_InterestExpenseDebt_F9258C0C7A5F4F08DADE69FD0ED53CC3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BenefitsLossesAndExpenses" xlink:label="loc_us-gaap_BenefitsLossesAndExpenses_C90C01C905EB07BCDE5869FD0ED5B4AA" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BenefitsLossesAndExpensesAbstract_A7AE10D795952678153969FD0ED45E14" xlink:to="loc_us-gaap_BenefitsLossesAndExpenses_C90C01C905EB07BCDE5869FD0ED5B4AA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_534944116051F47A6BCF69FD0ED51A52" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_534944116051F47A6BCF69FD0ED51A52" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_A54E2744ABAE67598AE369FD0ED589AD" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_A54E2744ABAE67598AE369FD0ED589AD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_68A07AE00347261A6CC669FD0ED5B5C5" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_68A07AE00347261A6CC669FD0ED5B5C5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_876EE0331ED1CA617CB569FD0ED532F1" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_876EE0331ED1CA617CB569FD0ED532F1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_FCED10F3471F2C19EFCD69FD0ED5556F" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_ProfitLoss_FCED10F3471F2C19EFCD69FD0ED5556F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_A127CBD19179D821D43069FD0ED5F213" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_A127CBD19179D821D43069FD0ED5F213" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_E171F2491351D2380B0069FD0ED536B4" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_E171F2491351D2380B0069FD0ED536B4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_1529FBA53BF233EE303869FD0ED5EFC9" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_1529FBA53BF233EE303869FD0ED5EFC9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_5D7266149F7FF5770D0769FD0ED58F0C" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_5D7266149F7FF5770D0769FD0ED58F0C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareAbstract" xlink:label="loc_us-gaap_EarningsPerShareAbstract_C69A318451D59338D57369FD0ED5A831" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_EarningsPerShareAbstract_C69A318451D59338D57369FD0ED5A831" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsPerBasicAndDilutedShare" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicAndDilutedShare_1397EE33A734FA2DEAE869FD0ED53780" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_C69A318451D59338D57369FD0ED5A831" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicAndDilutedShare_1397EE33A734FA2DEAE869FD0ED53780" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicAndDilutedShare" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicAndDilutedShare_22F0327957FA45835F9569FD0ED50468" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_C69A318451D59338D57369FD0ED5A831" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicAndDilutedShare_22F0327957FA45835F9569FD0ED50468" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasicAndDiluted" xlink:label="loc_us-gaap_EarningsPerShareBasicAndDiluted_432F39E7262BDA372FDE69FD0ED6F7F4" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_C69A318451D59338D57369FD0ED5A831" xlink:to="loc_us-gaap_EarningsPerShareBasicAndDiluted_432F39E7262BDA372FDE69FD0ED6F7F4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockDividendsPerShareCashPaid" xlink:label="loc_us-gaap_CommonStockDividendsPerShareCashPaid_B50D26EB7D29676C9E7A69FD0ED628DD" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_34C25698358D6B3CD53869FD0ED490E0" xlink:to="loc_us-gaap_CommonStockDividendsPerShareCashPaid_B50D26EB7D29676C9E7A69FD0ED628DD" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/ConsolidatingFinancialInformation" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/ConsolidatingFinancialInformationConsolidatingBalanceSheetDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CondensedFinancialStatementsCaptionsLineItems" xlink:label="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_05390E107D76D8B4502069FD0D58C0DA" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfCondensedFinancialStatementsTable" xlink:label="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_B4391BC0CC1ADEDB872D69FD0D57CDB2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_05390E107D76D8B4502069FD0D58C0DA" xlink:to="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_B4391BC0CC1ADEDB872D69FD0D57CDB2" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_9EE5C2CD87C11DF51EED69FD0D575399" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_B4391BC0CC1ADEDB872D69FD0D57CDB2" xlink:to="loc_dei_LegalEntityAxis_9EE5C2CD87C11DF51EED69FD0D575399" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_72A9946A74459E64BDFB69FD0D58165E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_9EE5C2CD87C11DF51EED69FD0D575399" xlink:to="loc_dei_EntityDomain_72A9946A74459E64BDFB69FD0D58165E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_72A9946A74459E64BDFB69FD0D58165E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_9EE5C2CD87C11DF51EED69FD0D575399" xlink:to="loc_dei_EntityDomain_72A9946A74459E64BDFB69FD0D58165E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ParentCompanyMember" xlink:label="loc_us-gaap_ParentCompanyMember_14A2DC20A70F1D0663C16AABE7CB2E46" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_72A9946A74459E64BDFB69FD0D58165E" xlink:to="loc_us-gaap_ParentCompanyMember_14A2DC20A70F1D0663C16AABE7CB2E46" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NonGuarantorSubsidiariesMember" xlink:label="loc_us-gaap_NonGuarantorSubsidiariesMember_BEF4AB83082D5712F2C669FD0D5871A9" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_72A9946A74459E64BDFB69FD0D58165E" xlink:to="loc_us-gaap_NonGuarantorSubsidiariesMember_BEF4AB83082D5712F2C669FD0D5871A9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsidiaryIssuerMember" xlink:label="loc_us-gaap_SubsidiaryIssuerMember_90921D01A9B361E977D769FD0D587FB1" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_72A9946A74459E64BDFB69FD0D58165E" xlink:to="loc_us-gaap_SubsidiaryIssuerMember_90921D01A9B361E977D769FD0D587FB1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConsolidationEliminationsMember" xlink:label="loc_us-gaap_ConsolidationEliminationsMember_7FA07C6BDDA3702B030669FD0D58E48B" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_72A9946A74459E64BDFB69FD0D58165E" xlink:to="loc_us-gaap_ConsolidationEliminationsMember_7FA07C6BDDA3702B030669FD0D58E48B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_05390E107D76D8B4502069FD0D58C0DA" xlink:to="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract" xlink:label="loc_us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract_0E16C0C1E14CA9CBC46669FD0D58ADC3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract_0E16C0C1E14CA9CBC46669FD0D58ADC3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesDebt" xlink:label="loc_us-gaap_TradingSecuritiesDebt_43B07F334D2C5ABDA28B69FD0D585D7B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract_0E16C0C1E14CA9CBC46669FD0D58ADC3" xlink:to="loc_us-gaap_TradingSecuritiesDebt_43B07F334D2C5ABDA28B69FD0D585D7B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShortTermInvestments" xlink:label="loc_us-gaap_ShortTermInvestments_1019639F2E3079E116E369FD0D5829D2" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract_0E16C0C1E14CA9CBC46669FD0D58ADC3" xlink:to="loc_us-gaap_ShortTermInvestments_1019639F2E3079E116E369FD0D5829D2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesEquity" xlink:label="loc_us-gaap_TradingSecuritiesEquity_829D326436108D0462BD69FD0D58D43B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract_0E16C0C1E14CA9CBC46669FD0D58ADC3" xlink:to="loc_us-gaap_TradingSecuritiesEquity_829D326436108D0462BD69FD0D58D43B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLongTermInvestments" xlink:label="loc_us-gaap_OtherLongTermInvestments_61FFF55EA8CE5C6B2CF869FD0D58B0A4" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract_0E16C0C1E14CA9CBC46669FD0D58ADC3" xlink:to="loc_us-gaap_OtherLongTermInvestments_61FFF55EA8CE5C6B2CF869FD0D58B0A4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherInvestments" xlink:label="loc_us-gaap_OtherInvestments_C0EAB9CADCC17B55B4ED69FD0D58130E" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract_0E16C0C1E14CA9CBC46669FD0D58ADC3" xlink:to="loc_us-gaap_OtherInvestments_C0EAB9CADCC17B55B4ED69FD0D58130E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Investments" xlink:label="loc_us-gaap_Investments_D9B1EDD40B3924D2C41469FD0D588043" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract_0E16C0C1E14CA9CBC46669FD0D58ADC3" xlink:to="loc_us-gaap_Investments_D9B1EDD40B3924D2C41469FD0D588043" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_209D45D698772A6D9C7169FD0D58390C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_209D45D698772A6D9C7169FD0D58390C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRecoverables" xlink:label="loc_us-gaap_ReinsuranceRecoverables_02FA938E319F5768F6BA69FD0D59E88E" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_ReinsuranceRecoverables_02FA938E319F5768F6BA69FD0D59E88E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PremiumsReceivableAtCarryingValue" xlink:label="loc_us-gaap_PremiumsReceivableAtCarryingValue_4077552C1EF4863F562C69FD0D5907C6" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_PremiumsReceivableAtCarryingValue_4077552C1EF4863F562C69FD0D5907C6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredPolicyAcquisitionCosts" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCosts_EDFD9DBC9B93217A4FA769FD0D594ED1" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_DeferredPolicyAcquisitionCosts_EDFD9DBC9B93217A4FA769FD0D594ED1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsLiabilitiesNet" xlink:label="loc_us-gaap_DeferredTaxAssetsLiabilitiesNet_99E5B1020B446DEB839A69FD0D595066" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_DeferredTaxAssetsLiabilitiesNet_99E5B1020B446DEB839A69FD0D595066" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccruedInvestmentIncomeReceivable" xlink:label="loc_us-gaap_AccruedInvestmentIncomeReceivable_AFC2B50A0DBE02F6F05469FD0D598094" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_AccruedInvestmentIncomeReceivable_AFC2B50A0DBE02F6F05469FD0D598094" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReceivablesFromBrokersDealersAndClearingOrganizations" xlink:label="loc_us-gaap_ReceivablesFromBrokersDealersAndClearingOrganizations_34F24263646156A265BA69FD0D590A36" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_ReceivablesFromBrokersDealersAndClearingOrganizations_34F24263646156A265BA69FD0D590A36" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityMethodInvestments" xlink:label="loc_us-gaap_EquityMethodInvestments_C7D1DCA162E025CE0F7369FD0D59B851" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_EquityMethodInvestments_C7D1DCA162E025CE0F7369FD0D59B851" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherAssets" xlink:label="loc_us-gaap_OtherAssets_D8853408B38DA120128569FD0D59D5F3" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_OtherAssets_D8853408B38DA120128569FD0D59D5F3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsHeldForSaleAtCarryingValue" xlink:label="loc_us-gaap_AssetsHeldForSaleAtCarryingValue_4ED992EC36E261A2540869FD0D59DCC6" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_AssetsHeldForSaleAtCarryingValue_4ED992EC36E261A2540869FD0D59DCC6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_1A5D0D8D362A1AA6A09569FD0D595A13" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_Assets_1A5D0D8D362A1AA6A09569FD0D595A13" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesAbstract" xlink:label="loc_us-gaap_LiabilitiesAbstract_0597CF9AB248D90CF0BA69FD0D590AF5" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_ADD691F4B0E1BBC68B6069FD0D581554" xlink:to="loc_us-gaap_LiabilitiesAbstract_0597CF9AB248D90CF0BA69FD0D590AF5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_0407FE94A7959B1F151B69FD0D5904E7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_0597CF9AB248D90CF0BA69FD0D590AF5" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_0407FE94A7959B1F151B69FD0D5904E7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_UnearnedPremiums" xlink:label="loc_us-gaap_UnearnedPremiums_1456AAA74FF5F0410FA969FD0D59209B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_0597CF9AB248D90CF0BA69FD0D590AF5" xlink:to="loc_us-gaap_UnearnedPremiums_1456AAA74FF5F0410FA969FD0D59209B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaap_LongTermDebt_EC01440D0D664AB963BC69FD0D591E51" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_0597CF9AB248D90CF0BA69FD0D590AF5" xlink:to="loc_us-gaap_LongTermDebt_EC01440D0D664AB963BC69FD0D591E51" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PayablesToBrokerDealersAndClearingOrganizations" xlink:label="loc_us-gaap_PayablesToBrokerDealersAndClearingOrganizations_DDFB3A929A5D577BF1AE69FD0D591F17" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_0597CF9AB248D90CF0BA69FD0D590AF5" xlink:to="loc_us-gaap_PayablesToBrokerDealersAndClearingOrganizations_DDFB3A929A5D577BF1AE69FD0D591F17" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLiabilities" xlink:label="loc_us-gaap_OtherLiabilities_A4FAB560C16F372EE39A69FD0D596566" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_0597CF9AB248D90CF0BA69FD0D590AF5" xlink:to="loc_us-gaap_OtherLiabilities_A4FAB560C16F372EE39A69FD0D596566" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesOfAssetsHeldForSale" xlink:label="loc_us-gaap_LiabilitiesOfAssetsHeldForSale_1BF4A6FF286E9A95908B69FD0D5AA836" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_0597CF9AB248D90CF0BA69FD0D590AF5" xlink:to="loc_us-gaap_LiabilitiesOfAssetsHeldForSale_1BF4A6FF286E9A95908B69FD0D5AA836" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaap_Liabilities_457FE0720CCAD868930669FD0D5A8D65" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_0597CF9AB248D90CF0BA69FD0D590AF5" xlink:to="loc_us-gaap_Liabilities_457FE0720CCAD868930669FD0D5A8D65" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityAbstract" xlink:label="loc_us-gaap_EquityAbstract_97A1E4890BC9D450C6ED69FD0D5AC21B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_05390E107D76D8B4502069FD0D58C0DA" xlink:to="loc_us-gaap_EquityAbstract_97A1E4890BC9D450C6ED69FD0D5AC21B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="loc_us-gaap_StockholdersEquity_715D57AF25007095924F69FD0D5A122D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_97A1E4890BC9D450C6ED69FD0D5AC21B" xlink:to="loc_us-gaap_StockholdersEquity_715D57AF25007095924F69FD0D5A122D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinorityInterest" xlink:label="loc_us-gaap_MinorityInterest_E04CF5A9F00D78BD5B0569FD0D5A3AD3" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_97A1E4890BC9D450C6ED69FD0D5AC21B" xlink:to="loc_us-gaap_MinorityInterest_E04CF5A9F00D78BD5B0569FD0D5A3AD3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_E94CB5499EAD4FFDC71769FD0D5ABA37" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_97A1E4890BC9D450C6ED69FD0D5AC21B" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_E94CB5499EAD4FFDC71769FD0D5ABA37" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_A6F9F93C1A6239F32D8069FD0D5ABFEF" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_97A1E4890BC9D450C6ED69FD0D5AC21B" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_A6F9F93C1A6239F32D8069FD0D5ABFEF" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/ConsolidatingFinancialInformationConsolidatingStatementOfCashFlowsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CondensedFinancialStatementsCaptionsLineItems" xlink:label="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_CAEDE63FCC3101E3BAE769FD0D2255F6" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfCondensedFinancialStatementsTable" xlink:label="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_4B871A00204D7B511A9869FD0D1B834C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_CAEDE63FCC3101E3BAE769FD0D2255F6" xlink:to="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_4B871A00204D7B511A9869FD0D1B834C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_7E0F5BF9219FB36AA7E069FD0D1C9DC8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_4B871A00204D7B511A9869FD0D1B834C" xlink:to="loc_dei_LegalEntityAxis_7E0F5BF9219FB36AA7E069FD0D1C9DC8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_72F6C983043703A64E9D69FD0D214D67_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_7E0F5BF9219FB36AA7E069FD0D1C9DC8" xlink:to="loc_dei_EntityDomain_72F6C983043703A64E9D69FD0D214D67_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_72F6C983043703A64E9D69FD0D214D67" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_7E0F5BF9219FB36AA7E069FD0D1C9DC8" xlink:to="loc_dei_EntityDomain_72F6C983043703A64E9D69FD0D214D67" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ParentCompanyMember" xlink:label="loc_us-gaap_ParentCompanyMember_57C801F32B016ADB08D36AAED6DB447E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_72F6C983043703A64E9D69FD0D214D67" xlink:to="loc_us-gaap_ParentCompanyMember_57C801F32B016ADB08D36AAED6DB447E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NonGuarantorSubsidiariesMember" xlink:label="loc_us-gaap_NonGuarantorSubsidiariesMember_653088A4D66B271314EE69FD0D22B77F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_72F6C983043703A64E9D69FD0D214D67" xlink:to="loc_us-gaap_NonGuarantorSubsidiariesMember_653088A4D66B271314EE69FD0D22B77F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsidiaryIssuerMember" xlink:label="loc_us-gaap_SubsidiaryIssuerMember_AF526988201A72DE596C69FD0D22720D" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_72F6C983043703A64E9D69FD0D214D67" xlink:to="loc_us-gaap_SubsidiaryIssuerMember_AF526988201A72DE596C69FD0D22720D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConsolidationEliminationsMember" xlink:label="loc_us-gaap_ConsolidationEliminationsMember_6D940117826DE70967FD69FD0D224737" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_72F6C983043703A64E9D69FD0D214D67" xlink:to="loc_us-gaap_ConsolidationEliminationsMember_6D940117826DE70967FD69FD0D224737" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_AA0D8CE0069AC602E93369FD0D227605" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_CAEDE63FCC3101E3BAE769FD0D2255F6" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_AA0D8CE0069AC602E93369FD0D227605" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_E6756B22DDE3047A96C669FD0D22B31E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_AA0D8CE0069AC602E93369FD0D227605" xlink:to="loc_us-gaap_ProfitLoss_E6756B22DDE3047A96C669FD0D22B31E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_AA0D8CE0069AC602E93369FD0D227605" xlink:to="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_08C0F31B0C11BF57275C69FD0D22F07E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_08C0F31B0C11BF57275C69FD0D22F07E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_F428DDBE4F115D5470DD69FD0D247B3C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_F428DDBE4F115D5470DD69FD0D247B3C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_B5038F1609D4648C021169FD0D2485DE" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_B5038F1609D4648C021169FD0D2485DE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GainLossOnInvestments" xlink:label="loc_us-gaap_GainLossOnInvestments_61BE0C20E0AD07912BD169FD0D24FB29" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_GainLossOnInvestments_61BE0C20E0AD07912BD169FD0D24FB29" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal" xlink:label="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_CFF05A591C38E6D8497269FD0D246088" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal_CFF05A591C38E6D8497269FD0D246088" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_0E1ACB76879BD5F4DD2F69FD0D241DEC" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_0E1ACB76879BD5F4DD2F69FD0D241DEC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries" xlink:label="loc_us-gaap_CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries_B297BFCC86CC154F57DA69FD0D242FA8" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries_B297BFCC86CC154F57DA69FD0D242FA8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E78A5EA1BB31BF4AC07769FD0D244780" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E78A5EA1BB31BF4AC07769FD0D244780" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInLossAndLossAdjustmentExpenseReserve" xlink:label="loc_us-gaap_IncreaseDecreaseInLossAndLossAdjustmentExpenseReserve_FE871A377B58222AF9CA69FD0D249FE2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E78A5EA1BB31BF4AC07769FD0D244780" xlink:to="loc_us-gaap_IncreaseDecreaseInLossAndLossAdjustmentExpenseReserve_FE871A377B58222AF9CA69FD0D249FE2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInUnearnedPremiums" xlink:label="loc_us-gaap_IncreaseDecreaseInUnearnedPremiums_9508EF85B5DCF5166BEC69FD0D244D06" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E78A5EA1BB31BF4AC07769FD0D244780" xlink:to="loc_us-gaap_IncreaseDecreaseInUnearnedPremiums_9508EF85B5DCF5166BEC69FD0D244D06" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInPremiumsReceivable" xlink:label="loc_us-gaap_IncreaseDecreaseInPremiumsReceivable_430ED6BDBDF0CD2A625C69FD0D24FBA6" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E78A5EA1BB31BF4AC07769FD0D244780" xlink:to="loc_us-gaap_IncreaseDecreaseInPremiumsReceivable_430ED6BDBDF0CD2A625C69FD0D24FBA6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInReinsuranceRecoverable" xlink:label="loc_us-gaap_IncreaseDecreaseInReinsuranceRecoverable_A170185441D8C25E72CF69FD0D24FABD" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E78A5EA1BB31BF4AC07769FD0D244780" xlink:to="loc_us-gaap_IncreaseDecreaseInReinsuranceRecoverable_A170185441D8C25E72CF69FD0D24FABD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_0E132D7B47864E85461D69FD0D24334D" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E78A5EA1BB31BF4AC07769FD0D244780" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet_0E132D7B47864E85461D69FD0D24334D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_70FB11143454F804FD1E69FD0D258DBC" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E78A5EA1BB31BF4AC07769FD0D244780" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_70FB11143454F804FD1E69FD0D258DBC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations" xlink:label="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_6A3453CCA97CC024977569FD0D251741" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E78A5EA1BB31BF4AC07769FD0D244780" xlink:to="loc_us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_6A3453CCA97CC024977569FD0D251741" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_F5CC4437D4523805A40469FD0D2564AB" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_E78A5EA1BB31BF4AC07769FD0D244780" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_F5CC4437D4523805A40469FD0D2564AB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsForProceedsFromShortTermInvestments" xlink:label="loc_us-gaap_PaymentsForProceedsFromShortTermInvestments_D053B6EFE3900BFEFBC069FD0D25EC4B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_us-gaap_PaymentsForProceedsFromShortTermInvestments_D053B6EFE3900BFEFBC069FD0D25EC4B" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ProceedsFromMaturitiesOfTradingSecuritiesDebt" xlink:label="loc_ob_ProceedsFromMaturitiesOfTradingSecuritiesDebt_AE52F10342D21295F73E69FD0D254FC0" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_ob_ProceedsFromMaturitiesOfTradingSecuritiesDebt_AE52F10342D21295F73E69FD0D254FC0" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ProceedsFromSaleOfTradingSecuritiesDebt" xlink:label="loc_ob_ProceedsFromSaleOfTradingSecuritiesDebt_84CCC7CE2838DDF0028B69FD0D25D0FC" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_ob_ProceedsFromSaleOfTradingSecuritiesDebt_84CCC7CE2838DDF0028B69FD0D25D0FC" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ProceedsFromSaleOfTradingCommonEquitySecurities" xlink:label="loc_ob_ProceedsFromSaleOfTradingCommonEquitySecurities_40F9BA6BFECDFDBE6F4769FD0D256260" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_ob_ProceedsFromSaleOfTradingCommonEquitySecurities_40F9BA6BFECDFDBE6F4769FD0D256260" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ProceedsFromSaleOfTradingSecuritiesConvertibleFixedMaturityInvestments" xlink:label="loc_ob_ProceedsFromSaleOfTradingSecuritiesConvertibleFixedMaturityInvestments_7E365940966364D4AA8B69FD0D25BF40" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_ob_ProceedsFromSaleOfTradingSecuritiesConvertibleFixedMaturityInvestments_7E365940966364D4AA8B69FD0D25BF40" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments" xlink:label="loc_us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments_DBEEDC2E362D3FF655E369FD0D25E43B" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments_DBEEDC2E362D3FF655E369FD0D25E43B" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PaymentsToAcquireTradingSecuritiesDebt" xlink:label="loc_ob_PaymentsToAcquireTradingSecuritiesDebt_F8C5A0C8FDF89E479E4369FD0D25F59C" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_ob_PaymentsToAcquireTradingSecuritiesDebt_F8C5A0C8FDF89E479E4369FD0D25F59C" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PaymentsToAcquireTradingCommonEquitySecurities" xlink:label="loc_ob_PaymentsToAcquireTradingCommonEquitySecurities_00ACE5C8EDC391E19BC569FD0D2516B5" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_ob_PaymentsToAcquireTradingCommonEquitySecurities_00ACE5C8EDC391E19BC569FD0D2516B5" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PaymentsToAcquireTradingSecuritiesConvertibleFixedMaturityInvestments" xlink:label="loc_ob_PaymentsToAcquireTradingSecuritiesConvertibleFixedMaturityInvestments_5F61C1A5BE4BA4E20F8769FD0D26DCE7" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_ob_PaymentsToAcquireTradingSecuritiesConvertibleFixedMaturityInvestments_5F61C1A5BE4BA4E20F8769FD0D26DCE7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireOtherInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireOtherInvestments_2B20FB83EAF455CDC83A69FD0D26B2B1" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_us-gaap_PaymentsToAcquireOtherInvestments_2B20FB83EAF455CDC83A69FD0D26B2B1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_ED3FF04D5B9A5D93938869FD0D26D336" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_ED3FF04D5B9A5D93938869FD0D26D336" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_IncreaseDecreaseInUnsettledAccountsReceivableAndAccountsPayable" xlink:label="loc_ob_IncreaseDecreaseInUnsettledAccountsReceivableAndAccountsPayable_730B2E0EB8923960043F69FD0D26C80A" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_ob_IncreaseDecreaseInUnsettledAccountsReceivableAndAccountsPayable_730B2E0EB8923960043F69FD0D26C80A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_5A859A6BEF8F58C4780E69FD0D26A43C" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_5A859A6BEF8F58C4780E69FD0D26A43C" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CashPaidToParentCompanyByConsolidatedSubsidiariesReturnOfCapital" xlink:label="loc_ob_CashPaidToParentCompanyByConsolidatedSubsidiariesReturnOfCapital_E4204C7D7A43037DBC9A69FD0D26FD83" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_ob_CashPaidToParentCompanyByConsolidatedSubsidiariesReturnOfCapital_E4204C7D7A43037DBC9A69FD0D26FD83" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations_1ACAE05910852009009769FD0D261357" xlink:type="locator" />
    <definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations_1ACAE05910852009009769FD0D261357" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations" xlink:label="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_2FC1587DD832FC32FEBB69FD0D2673F2" xlink:type="locator" />
    <definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_2FC1587DD832FC32FEBB69FD0D2673F2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_77487B718ADE29D7F2A769FD0D26E2A2" xlink:type="locator" />
    <definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_53BADE784AA8898686BC69FD0D2563EB" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_77487B718ADE29D7F2A769FD0D26E2A2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_ADCB1F28E6CBC7B10B3D69FD0D265E7A" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_ADCB1F28E6CBC7B10B3D69FD0D265E7A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsOfDividendsCommonStock" xlink:label="loc_us-gaap_PaymentsOfDividendsCommonStock_E70F7A04A1153A2977E269FD0D263038" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_ADCB1F28E6CBC7B10B3D69FD0D265E7A" xlink:to="loc_us-gaap_PaymentsOfDividendsCommonStock_E70F7A04A1153A2977E269FD0D263038" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashDividendsPaidToParentCompany" xlink:label="loc_us-gaap_CashDividendsPaidToParentCompany_CD0C88B2E0592C954D8D69FD0D263D7C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_ADCB1F28E6CBC7B10B3D69FD0D265E7A" xlink:to="loc_us-gaap_CashDividendsPaidToParentCompany_CD0C88B2E0592C954D8D69FD0D263D7C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_6F129164A7138BED86F069FD0D26936A" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_ADCB1F28E6CBC7B10B3D69FD0D265E7A" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_6F129164A7138BED86F069FD0D26936A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ProceedsFromSaleOfSubsidiary" xlink:label="loc_ob_ProceedsFromSaleOfSubsidiary_AB6A86F0C2DAAA6EA6AC69FD0D26C21E" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_ADCB1F28E6CBC7B10B3D69FD0D265E7A" xlink:to="loc_ob_ProceedsFromSaleOfSubsidiary_AB6A86F0C2DAAA6EA6AC69FD0D26C21E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations_8B528BC2B192A722921069FD0D2778AD" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_ADCB1F28E6CBC7B10B3D69FD0D265E7A" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations_8B528BC2B192A722921069FD0D2778AD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashProvidedByUsedInFinancingActivitiesDiscontinuedOperations" xlink:label="loc_us-gaap_CashProvidedByUsedInFinancingActivitiesDiscontinuedOperations_69F33A1549D236601F2A69FD0D271AF7" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_CashProvidedByUsedInFinancingActivitiesDiscontinuedOperations_69F33A1549D236601F2A69FD0D271AF7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_78198B9C9436394F029D69FD0D27962B" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_78198B9C9436394F029D69FD0D27962B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_0B6D83AF26E98C07653569FD0D27DCE9" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_0B6D83AF26E98C07653569FD0D27DCE9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_27AADC707BF1CF8C252169FD0D277D06" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_EE549DB7F180BD5D3E9569FD0D22EA15" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_27AADC707BF1CF8C252169FD0D277D06" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromContributedCapital" xlink:label="loc_us-gaap_ProceedsFromContributedCapital_6EFE0D72595FCDEC511A69FD0D27724C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_CAEDE63FCC3101E3BAE769FD0D2255F6" xlink:to="loc_us-gaap_ProceedsFromContributedCapital_6EFE0D72595FCDEC511A69FD0D27724C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromIssuanceOfDebt" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_8F428A65713BFEFA939969FD0D270FDC" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_CAEDE63FCC3101E3BAE769FD0D2255F6" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_8F428A65713BFEFA939969FD0D270FDC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:label="loc_us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_491057F8CC72A11B5CE969FD0D27661D" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_CAEDE63FCC3101E3BAE769FD0D2255F6" xlink:to="loc_us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_491057F8CC72A11B5CE969FD0D27661D" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/ConsolidatingFinancialInformationConsolidatingStatementOfOperationsAndComprehensiveLossDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CondensedFinancialStatementsCaptionsLineItems" xlink:label="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfCondensedFinancialStatementsTable" xlink:label="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_9C13250B6D7378F87BF869FD0D4B7103" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_9C13250B6D7378F87BF869FD0D4B7103" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_1F97DD691E4AE40C98B869FD0D4BDCDE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCondensedFinancialStatementsTable_9C13250B6D7378F87BF869FD0D4B7103" xlink:to="loc_dei_LegalEntityAxis_1F97DD691E4AE40C98B869FD0D4BDCDE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_91E2DEF0A9F2A45695E169FD0D4B5E04_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_1F97DD691E4AE40C98B869FD0D4BDCDE" xlink:to="loc_dei_EntityDomain_91E2DEF0A9F2A45695E169FD0D4B5E04_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_91E2DEF0A9F2A45695E169FD0D4B5E04" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_1F97DD691E4AE40C98B869FD0D4BDCDE" xlink:to="loc_dei_EntityDomain_91E2DEF0A9F2A45695E169FD0D4B5E04" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ParentCompanyMember" xlink:label="loc_us-gaap_ParentCompanyMember_2292127AAB51269A55DE6AAD10BAB510" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_91E2DEF0A9F2A45695E169FD0D4B5E04" xlink:to="loc_us-gaap_ParentCompanyMember_2292127AAB51269A55DE6AAD10BAB510" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NonGuarantorSubsidiariesMember" xlink:label="loc_us-gaap_NonGuarantorSubsidiariesMember_0A5B987A97D62A58260969FD0D4B91F2" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_91E2DEF0A9F2A45695E169FD0D4B5E04" xlink:to="loc_us-gaap_NonGuarantorSubsidiariesMember_0A5B987A97D62A58260969FD0D4B91F2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsidiaryIssuerMember" xlink:label="loc_us-gaap_SubsidiaryIssuerMember_B7EA75E34532E932D76769FD0D4B9073" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_91E2DEF0A9F2A45695E169FD0D4B5E04" xlink:to="loc_us-gaap_SubsidiaryIssuerMember_B7EA75E34532E932D76769FD0D4B9073" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConsolidationEliminationsMember" xlink:label="loc_us-gaap_ConsolidationEliminationsMember_C209BF4E97942EC9B2AF69FD0D4B2C0C" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_91E2DEF0A9F2A45695E169FD0D4B5E04" xlink:to="loc_us-gaap_ConsolidationEliminationsMember_C209BF4E97942EC9B2AF69FD0D4B2C0C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RevenuesAbstract" xlink:label="loc_us-gaap_RevenuesAbstract_12266EC5C2E4A43C571469FD0D4B067D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_RevenuesAbstract_12266EC5C2E4A43C571469FD0D4B067D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PremiumsEarnedNet" xlink:label="loc_us-gaap_PremiumsEarnedNet_5DF34A16737FF90408F969FD0D4BFF1D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_12266EC5C2E4A43C571469FD0D4B067D" xlink:to="loc_us-gaap_PremiumsEarnedNet_5DF34A16737FF90408F969FD0D4BFF1D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetInvestmentIncome" xlink:label="loc_us-gaap_NetInvestmentIncome_2633D4A223A9A51BD97969FD0D4C21E2" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_12266EC5C2E4A43C571469FD0D4B067D" xlink:to="loc_us-gaap_NetInvestmentIncome_2633D4A223A9A51BD97969FD0D4C21E2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GainLossOnInvestments" xlink:label="loc_us-gaap_GainLossOnInvestments_00DAA7FBED50BBC0578A69FD0D4C690B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_12266EC5C2E4A43C571469FD0D4B067D" xlink:to="loc_us-gaap_GainLossOnInvestments_00DAA7FBED50BBC0578A69FD0D4C690B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_7C5C5859E932AAAE914069FD0D4C2C18" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_12266EC5C2E4A43C571469FD0D4B067D" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_7C5C5859E932AAAE914069FD0D4C2C18" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_15E23C73FC8CC0679D1769FD0D4C42EC" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_12266EC5C2E4A43C571469FD0D4B067D" xlink:to="loc_us-gaap_Revenues_15E23C73FC8CC0679D1769FD0D4C42EC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingExpensesAbstract" xlink:label="loc_us-gaap_OperatingExpensesAbstract_97BC0523E8EDFFCE5E8E69FD0D4C2E78" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_12266EC5C2E4A43C571469FD0D4B067D" xlink:to="loc_us-gaap_OperatingExpensesAbstract_97BC0523E8EDFFCE5E8E69FD0D4C2E78" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PolicyholderBenefitsAndClaimsIncurredNet" xlink:label="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_1201F3D3FF1C8DF5E28769FD0D4CF3CD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_97BC0523E8EDFFCE5E8E69FD0D4C2E78" xlink:to="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_1201F3D3FF1C8DF5E28769FD0D4CF3CD" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InsuranceAndReinsuranceAcquisitionExpenses" xlink:label="loc_ob_InsuranceAndReinsuranceAcquisitionExpenses_527D776FDF0932A8AD4C69FD0D4C4173" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_97BC0523E8EDFFCE5E8E69FD0D4C2E78" xlink:to="loc_ob_InsuranceAndReinsuranceAcquisitionExpenses_527D776FDF0932A8AD4C69FD0D4C4173" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherUnderwritingExpense" xlink:label="loc_us-gaap_OtherUnderwritingExpense_FE8FEFCA793D2DD8F6DB69FD0D4C59E2" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_97BC0523E8EDFFCE5E8E69FD0D4C2E78" xlink:to="loc_us-gaap_OtherUnderwritingExpense_FE8FEFCA793D2DD8F6DB69FD0D4C59E2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_0EDD125EA51AB94525A769FD0D4C9647" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_97BC0523E8EDFFCE5E8E69FD0D4C2E78" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_0EDD125EA51AB94525A769FD0D4C9647" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestExpenseDebt" xlink:label="loc_us-gaap_InterestExpenseDebt_1D37F152FD7744632E5769FD0D4CDDBF" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_97BC0523E8EDFFCE5E8E69FD0D4C2E78" xlink:to="loc_us-gaap_InterestExpenseDebt_1D37F152FD7744632E5769FD0D4CDDBF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BenefitsLossesAndExpenses" xlink:label="loc_us-gaap_BenefitsLossesAndExpenses_0EA058899085D7FBEB4269FD0D4C4546" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_97BC0523E8EDFFCE5E8E69FD0D4C2E78" xlink:to="loc_us-gaap_BenefitsLossesAndExpenses_0EA058899085D7FBEB4269FD0D4C4546" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_3914D39A1314A919B1BF69FD0D4D6786" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_3914D39A1314A919B1BF69FD0D4D6786" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_4ACACC13C1D3FAFA6E6069FD0D4D7485" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_4ACACC13C1D3FAFA6E6069FD0D4D7485" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_24EBBF98C665BAD6FBA569FD0D4D7105" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_24EBBF98C665BAD6FBA569FD0D4D7105" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_AF84C36C1A50F019446E69FD0D4D1373" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_AF84C36C1A50F019446E69FD0D4D1373" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_F82688A279F801E2C96769FD0D4D091B" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_F82688A279F801E2C96769FD0D4D091B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossBeforeExtraordinaryItemsAndCumulativeEffectOfChangeInAccountingPrinciple" xlink:label="loc_us-gaap_IncomeLossBeforeExtraordinaryItemsAndCumulativeEffectOfChangeInAccountingPrinciple_CD1688054AA7E51C7CE769FD0D4D2AD1" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_IncomeLossBeforeExtraordinaryItemsAndCumulativeEffectOfChangeInAccountingPrinciple_CD1688054AA7E51C7CE769FD0D4D2AD1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_2B2570C56D5EC15B724A69FD0D4D28B5" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_2B2570C56D5EC15B724A69FD0D4D28B5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProfitLoss" xlink:label="loc_us-gaap_ProfitLoss_ED7A2D4D6251074A4D2869FD0D4DFE58" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_ProfitLoss_ED7A2D4D6251074A4D2869FD0D4DFE58" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_FB4F0AC9779FB266F80E69FD0D4D0A5F" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_FB4F0AC9779FB266F80E69FD0D4D0A5F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_E51D1AD86D7CC217B9DC69FD0D4DF8F9" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_E51D1AD86D7CC217B9DC69FD0D4DF8F9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_87FB9BE69900057963E569FD0D4D618F" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax_87FB9BE69900057963E569FD0D4D618F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_1EAF2577E35D886D7D6869FD0D4D5369" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CondensedFinancialStatementsCaptionsLineItems_9E617A07AFE408B5EBAE69FD0D4B43C0" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_1EAF2577E35D886D7D6869FD0D4D5369" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/ConsolidatingFinancialInformationTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/Debt" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/DebtDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="loc_us-gaap_DebtInstrumentTable_1F6E44A5F9EE036786D569FD0E093C34" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:to="loc_us-gaap_DebtInstrumentTable_1F6E44A5F9EE036786D569FD0E093C34" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_F898C09133BE1ED2A74A69FD0E097550" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_1F6E44A5F9EE036786D569FD0E093C34" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_F898C09133BE1ED2A74A69FD0E097550" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_ADB1EABA8128B570C4B36AA8EDF313FB_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_F898C09133BE1ED2A74A69FD0E097550" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_ADB1EABA8128B570C4B36AA8EDF313FB_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BB6F754FA1210CFC4F9E69FD0E09BA98" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_F898C09133BE1ED2A74A69FD0E097550" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BB6F754FA1210CFC4F9E69FD0E09BA98" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_ADB1EABA8128B570C4B36AA8EDF313FB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BB6F754FA1210CFC4F9E69FD0E09BA98" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_ADB1EABA8128B570C4B36AA8EDF313FB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_E7755C670B741D598F1F69FD0E0996FC" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_BB6F754FA1210CFC4F9E69FD0E09BA98" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_E7755C670B741D598F1F69FD0E0996FC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_7A21AFCFEF53311B0C7F69FD0E09E6EF" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_1F6E44A5F9EE036786D569FD0E093C34" xlink:to="loc_us-gaap_DebtInstrumentAxis_7A21AFCFEF53311B0C7F69FD0E09E6EF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_357BD5BB2E0265CE687869FD0E099A33_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_7A21AFCFEF53311B0C7F69FD0E09E6EF" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_357BD5BB2E0265CE687869FD0E099A33_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_357BD5BB2E0265CE687869FD0E099A33" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_7A21AFCFEF53311B0C7F69FD0E09E6EF" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_357BD5BB2E0265CE687869FD0E099A33" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ObhSeniorNotesMember" xlink:label="loc_ob_ObhSeniorNotesMember_450275FBF2246CFB9E1069FD0E094C7D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_357BD5BB2E0265CE687869FD0E099A33" xlink:to="loc_ob_ObhSeniorNotesMember_450275FBF2246CFB9E1069FD0E094C7D" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_A2012ObhSeniorNotesMember" xlink:label="loc_ob_A2012ObhSeniorNotesMember_6650B85D30E1B0B26A5F69FD0E0961E4" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_357BD5BB2E0265CE687869FD0E099A33" xlink:to="loc_ob_A2012ObhSeniorNotesMember_6650B85D30E1B0B26A5F69FD0E0961E4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_6C409FE5B0F029C8993A69FD0E09B610" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_1F6E44A5F9EE036786D569FD0E093C34" xlink:to="loc_dei_LegalEntityAxis_6C409FE5B0F029C8993A69FD0E09B610" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_CF9999BA5008DDC041CB69FD0E09E41D_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_6C409FE5B0F029C8993A69FD0E09B610" xlink:to="loc_dei_EntityDomain_CF9999BA5008DDC041CB69FD0E09E41D_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_CF9999BA5008DDC041CB69FD0E09E41D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_6C409FE5B0F029C8993A69FD0E09B610" xlink:to="loc_dei_EntityDomain_CF9999BA5008DDC041CB69FD0E09E41D" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_OnebeaconUSHoldingsIncMember" xlink:label="loc_ob_OnebeaconUSHoldingsIncMember_106C78EE9D8941170EB469FD0E0ABBC6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_CF9999BA5008DDC041CB69FD0E09E41D" xlink:to="loc_ob_OnebeaconUSHoldingsIncMember_106C78EE9D8941170EB469FD0E0ABBC6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_C105268D1A9D7107AD0969FD0E0A2F2F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_C105268D1A9D7107AD0969FD0E0A2F2F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentUnamortizedDiscount" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_8350B0A6F0529ADBD76169FD0E0A7A76" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_8350B0A6F0529ADBD76169FD0E0A7A76" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtAndCapitalLeaseObligations" xlink:label="loc_us-gaap_DebtAndCapitalLeaseObligations_DB297EB6EB432C8044FC69FD0E0AAE1A" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:to="loc_us-gaap_DebtAndCapitalLeaseObligations_DB297EB6EB432C8044FC69FD0E0AAE1A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_DebtInstrumentIssuePriceAsPercentageOfParValue" xlink:label="loc_ob_DebtInstrumentIssuePriceAsPercentageOfParValue_E4625B07990484EA9DCF69FD0E0AF997" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:to="loc_ob_DebtInstrumentIssuePriceAsPercentageOfParValue_E4625B07990484EA9DCF69FD0E0AF997" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromIssuanceOfDebt" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_65DEA4507F4F28CDF8A869FD0E0A4D82" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_65DEA4507F4F28CDF8A869FD0E0A4D82" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_72CE0AA8C8FC1A8FEF6A69FD0E0AE1BB" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_72CE0AA8C8FC1A8FEF6A69FD0E0AE1BB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredFinanceCostsGross" xlink:label="loc_us-gaap_DeferredFinanceCostsGross_8CA3FF793178E28E5A4669FD0E0A59D1" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:to="loc_us-gaap_DeferredFinanceCostsGross_8CA3FF793178E28E5A4669FD0E0A59D1" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_DeferredUnderwritingDiscountGross" xlink:label="loc_ob_DeferredUnderwritingDiscountGross_61AC993104983D5F11C869FD0E0A3538" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:to="loc_ob_DeferredUnderwritingDiscountGross_61AC993104983D5F11C869FD0E0A3538" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_344F3FD36FC849541A9569FD0E0A5F65" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_344F3FD36FC849541A9569FD0E0A5F65" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaap_LongTermDebt_F867C3051FC97BE8792F69FD0E0AF0B0" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_1192BE5BA01ED371894B69FD0E0A413F" xlink:to="loc_us-gaap_LongTermDebt_F867C3051FC97BE8792F69FD0E0AF0B0" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/DebtTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/DiscontinuedOperations" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/DiscontinuedOperationsAdditionalDisclosuresDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_CE88730913298605B13B6E96634F669E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_CE88730913298605B13B6E96634F669E" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_36665519ACB9742B00DA6EB87CDC2340" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_CE88730913298605B13B6E96634F669E" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_36665519ACB9742B00DA6EB87CDC2340" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_9CC42C3D7FCB227F1D0B6EB87CFB7B9B_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_36665519ACB9742B00DA6EB87CDC2340" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_9CC42C3D7FCB227F1D0B6EB87CFB7B9B_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_9CC42C3D7FCB227F1D0B6EB87CFB7B9B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_36665519ACB9742B00DA6EB87CDC2340" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_9CC42C3D7FCB227F1D0B6EB87CFB7B9B" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SurplusNotesForSaleOfDiscontinuedOperationsMember" xlink:label="loc_ob_SurplusNotesForSaleOfDiscontinuedOperationsMember_38CC82EAD702B8633DE36EB8E7EDF7F4" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_9CC42C3D7FCB227F1D0B6EB87CFB7B9B" xlink:to="loc_ob_SurplusNotesForSaleOfDiscontinuedOperationsMember_38CC82EAD702B8633DE36EB8E7EDF7F4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementScenarioAxis" xlink:label="loc_us-gaap_StatementScenarioAxis_F241AAA3375A8D1B49946E96634F8ED0" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_CE88730913298605B13B6E96634F669E" xlink:to="loc_us-gaap_StatementScenarioAxis_F241AAA3375A8D1B49946E96634F8ED0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_3604338C15D7DBB5882B6E96634F132F_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementScenarioAxis_F241AAA3375A8D1B49946E96634F8ED0" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_3604338C15D7DBB5882B6E96634F132F_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="loc_us-gaap_ScenarioUnspecifiedDomain_3604338C15D7DBB5882B6E96634F132F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementScenarioAxis_F241AAA3375A8D1B49946E96634F8ED0" xlink:to="loc_us-gaap_ScenarioUnspecifiedDomain_3604338C15D7DBB5882B6E96634F132F" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_EconomicEntityAxis" xlink:label="loc_ob_EconomicEntityAxis_5F4A45DCB117DD0B94EE6E96634FB7C6" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_CE88730913298605B13B6E96634F669E" xlink:to="loc_ob_EconomicEntityAxis_5F4A45DCB117DD0B94EE6E96634FB7C6" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_EconomicEntityDomain" xlink:label="loc_ob_EconomicEntityDomain_E708B4D1330B7733EAA56E96634F4FE3_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ob_EconomicEntityAxis_5F4A45DCB117DD0B94EE6E96634FB7C6" xlink:to="loc_ob_EconomicEntityDomain_E708B4D1330B7733EAA56E96634F4FE3_default" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_EconomicEntityDomain" xlink:label="loc_ob_EconomicEntityDomain_E708B4D1330B7733EAA56E96634F4FE3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ob_EconomicEntityAxis_5F4A45DCB117DD0B94EE6E96634FB7C6" xlink:to="loc_ob_EconomicEntityDomain_E708B4D1330B7733EAA56E96634F4FE3" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_GeneralReinsuranceCorporationCoverMember" xlink:label="loc_ob_GeneralReinsuranceCorporationCoverMember_BB06E262035AC41297E46E96634FFE1B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_EconomicEntityDomain_E708B4D1330B7733EAA56E96634F4FE3" xlink:to="loc_ob_GeneralReinsuranceCorporationCoverMember_BB06E262035AC41297E46E96634FFE1B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_5B006C0DBCD0F336DA5E6E96634F6F80" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_CE88730913298605B13B6E96634F669E" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_5B006C0DBCD0F336DA5E6E96634F6F80" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_BB248DF57AD2F0A120856E96634FE4C2_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_5B006C0DBCD0F336DA5E6E96634F6F80" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_BB248DF57AD2F0A120856E96634FE4C2_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_BB248DF57AD2F0A120856E96634FE4C2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_5B006C0DBCD0F336DA5E6E96634F6F80" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_BB248DF57AD2F0A120856E96634FE4C2" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RunoffMember" xlink:label="loc_ob_RunoffMember_C24D3AA95432C544CCD86E96634F1D89" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_BB248DF57AD2F0A120856E96634FE4C2" xlink:to="loc_ob_RunoffMember_C24D3AA95432C544CCD86E96634F1D89" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_A84534C22435FE26F2786E96634F68E8" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_CE88730913298605B13B6E96634F669E" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_A84534C22435FE26F2786E96634F68E8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_D0FEFE0E2C32178723D06E96634F77D1_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_A84534C22435FE26F2786E96634F68E8" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_D0FEFE0E2C32178723D06E96634F77D1_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_D0FEFE0E2C32178723D06E96634F77D1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_A84534C22435FE26F2786E96634F68E8" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_D0FEFE0E2C32178723D06E96634F77D1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDiscontinuedOperationsMember" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_7870FC44AFF3161FBCCF6E96634F04CD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_D0FEFE0E2C32178723D06E96634F77D1" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_7870FC44AFF3161FBCCF6E96634F04CD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CededCreditRiskAxis" xlink:label="loc_us-gaap_CededCreditRiskAxis_DC1660FCFBC87AC00B0D6E96634F6A60" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_CE88730913298605B13B6E96634F669E" xlink:to="loc_us-gaap_CededCreditRiskAxis_DC1660FCFBC87AC00B0D6E96634F6A60" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CededCreditRiskReinsurerDomain" xlink:label="loc_us-gaap_CededCreditRiskReinsurerDomain_F49D15CCF7137463982D6E96634FC50C_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CededCreditRiskAxis_DC1660FCFBC87AC00B0D6E96634F6A60" xlink:to="loc_us-gaap_CededCreditRiskReinsurerDomain_F49D15CCF7137463982D6E96634FC50C_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CededCreditRiskReinsurerDomain" xlink:label="loc_us-gaap_CededCreditRiskReinsurerDomain_F49D15CCF7137463982D6E96634FC50C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CededCreditRiskAxis_DC1660FCFBC87AC00B0D6E96634F6A60" xlink:to="loc_us-gaap_CededCreditRiskReinsurerDomain_F49D15CCF7137463982D6E96634FC50C" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_NationalIndemnityCompanyAndGeneralReinsuranceCorporationMember" xlink:label="loc_ob_NationalIndemnityCompanyAndGeneralReinsuranceCorporationMember_D0086F9A785A7C41A7426E96634F2242" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CededCreditRiskReinsurerDomain_F49D15CCF7137463982D6E96634FC50C" xlink:to="loc_ob_NationalIndemnityCompanyAndGeneralReinsuranceCorporationMember_D0086F9A785A7C41A7426E96634F2242" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_HanoverInsuranceCompanyMember" xlink:label="loc_ob_HanoverInsuranceCompanyMember_285BA9EDA2DC4085E8E36E96634FE478" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CededCreditRiskReinsurerDomain_F49D15CCF7137463982D6E96634FC50C" xlink:to="loc_ob_HanoverInsuranceCompanyMember_285BA9EDA2DC4085E8E36E96634FE478" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TokioMarineAndNichidoFireMember" xlink:label="loc_ob_TokioMarineAndNichidoFireMember_5AA314341B16B3F7937B6E96634FB3F5" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CededCreditRiskReinsurerDomain_F49D15CCF7137463982D6E96634FC50C" xlink:to="loc_ob_TokioMarineAndNichidoFireMember_5AA314341B16B3F7937B6E96634FB3F5" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_MunichReinsuranceAmericaMember" xlink:label="loc_ob_MunichReinsuranceAmericaMember_F1CF30F6094BDE3EC13F6E96634F3523" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CededCreditRiskReinsurerDomain_F49D15CCF7137463982D6E96634FC50C" xlink:to="loc_ob_MunichReinsuranceAmericaMember_F1CF30F6094BDE3EC13F6E96634F3523" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_EverestReinsuranceMember" xlink:label="loc_ob_EverestReinsuranceMember_3B9CDB3F93906E8F51656E96634FACF6" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CededCreditRiskReinsurerDomain_F49D15CCF7137463982D6E96634FC50C" xlink:to="loc_ob_EverestReinsuranceMember_3B9CDB3F93906E8F51656E96634FACF6" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ReinsuranceContractByNatureAxis" xlink:label="loc_ob_ReinsuranceContractByNatureAxis_87E9445D0BF9C2E90DA56E96634F9915" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_CE88730913298605B13B6E96634F669E" xlink:to="loc_ob_ReinsuranceContractByNatureAxis_87E9445D0BF9C2E90DA56E96634F9915" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ReinsuranceContractNameDomain" xlink:label="loc_ob_ReinsuranceContractNameDomain_08A314376EDBBBD74E4A6E96634FC31C_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ob_ReinsuranceContractByNatureAxis_87E9445D0BF9C2E90DA56E96634F9915" xlink:to="loc_ob_ReinsuranceContractNameDomain_08A314376EDBBBD74E4A6E96634FC31C_default" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ReinsuranceContractNameDomain" xlink:label="loc_ob_ReinsuranceContractNameDomain_08A314376EDBBBD74E4A6E96634FC31C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ob_ReinsuranceContractByNatureAxis_87E9445D0BF9C2E90DA56E96634F9915" xlink:to="loc_ob_ReinsuranceContractNameDomain_08A314376EDBBBD74E4A6E96634FC31C" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_GRCCoverMember" xlink:label="loc_ob_GRCCoverMember_5AA00EA3E880AEC56DA36E96634FA749" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_ReinsuranceContractNameDomain_08A314376EDBBBD74E4A6E96634FC31C" xlink:to="loc_ob_GRCCoverMember_5AA00EA3E880AEC56DA36E96634FA749" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_GeneralReinsuranceCorporationCoverMember" xlink:label="loc_ob_GeneralReinsuranceCorporationCoverMember_0A9E41DF32009DE2641C6E96634FB31F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_ReinsuranceContractNameDomain_08A314376EDBBBD74E4A6E96634FC31C" xlink:to="loc_ob_GeneralReinsuranceCorporationCoverMember_0A9E41DF32009DE2641C6E96634FB31F" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_NICOCoverMember" xlink:label="loc_ob_NICOCoverMember_923C58C5C9813DA73A246E96634F7356" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_ReinsuranceContractNameDomain_08A314376EDBBBD74E4A6E96634FC31C" xlink:to="loc_ob_NICOCoverMember_923C58C5C9813DA73A246E96634F7356" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ChangeInSurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations" xlink:label="loc_ob_ChangeInSurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations_28C822B688BF3C874B2F6EAB5CE59480" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_ob_ChangeInSurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations_28C822B688BF3C874B2F6EAB5CE59480" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations" xlink:label="loc_ob_SurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations_8B4C61A0BF06EFDFDCC26EA6D33520C2" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_ob_SurplusNotesIssuedAsSellerFinancingInSaleOfDiscontinuedOperations_8B4C61A0BF06EFDFDCC26EA6D33520C2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_10FAAC8A76E738BD398F6E96634FA654" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_10FAAC8A76E738BD398F6E96634FA654" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_QuotaShareReinsuranceAgreementPercentage" xlink:label="loc_ob_QuotaShareReinsuranceAgreementPercentage_829FB1290F07E005275A6E96634F7151" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_ob_QuotaShareReinsuranceAgreementPercentage_829FB1290F07E005275A6E96634F7151" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRecoverablesGross" xlink:label="loc_us-gaap_ReinsuranceRecoverablesGross_010AF80C71AA965C573B6E96634F7D8F" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_ReinsuranceRecoverablesGross_010AF80C71AA965C573B6E96634F7D8F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims" xlink:label="loc_us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims_1A53BBB71FB124DC76816E96634F0B39" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims_1A53BBB71FB124DC76816E96634F0B39" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_6B25200956BC7DC3CAD96E96634F9779" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_6B25200956BC7DC3CAD96E96634F9779" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_4FC2F71E369A1B98C6016E96634F40F7" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_4FC2F71E369A1B98C6016E96634F40F7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_8113BDE6DBF31C3942826E96634F7605" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_8113BDE6DBF31C3942826E96634F7605" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_4EDBD4DB8CCAC2E4EFAF6E96634FB497" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_4EDBD4DB8CCAC2E4EFAF6E96634FB497" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherIncome" xlink:label="loc_us-gaap_OtherIncome_A92F33A09F7AB7DDEEB26E96634FAF76" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_OtherIncome_A92F33A09F7AB7DDEEB26E96634FAF76" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet_CB6C67B48AD6E5D5F8806E96634FC152" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet_CB6C67B48AD6E5D5F8806E96634FC152" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseClaimsPaidDiscontinuedOperations" xlink:label="loc_ob_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseClaimsPaidDiscontinuedOperations_8C9CA0173C7DAF53DE1A6E96634F0802" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_ob_LiabilityforUnpaidClaimsandClaimsAdjustmentExpenseClaimsPaidDiscontinuedOperations_8C9CA0173C7DAF53DE1A6E96634F0802" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PolicyholderBenefitsAndClaimsIncurredNet" xlink:label="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_473B42046672BE963D316E96634F3417" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_473B42046672BE963D316E96634F3417" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_36269806F2B8474254C16E96634FA436" xlink:type="locator" />
    <definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_36269806F2B8474254C16E96634FA436" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CausesOfIncreaseDecreaseInLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseAmount" xlink:label="loc_us-gaap_CausesOfIncreaseDecreaseInLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseAmount_C54DF7C4BD4D13CEDC926E96634F7589" xlink:type="locator" />
    <definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_CausesOfIncreaseDecreaseInLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseAmount_C54DF7C4BD4D13CEDC926E96634F7589" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CausesOfIncreaseDecreaseInLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseAmountnetoftax" xlink:label="loc_ob_CausesOfIncreaseDecreaseInLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseAmountnetoftax_CC9689132B630349AAB56E9981BF7F0E" xlink:type="locator" />
    <definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_ob_CausesOfIncreaseDecreaseInLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseAmountnetoftax_CC9689132B630349AAB56E9981BF7F0E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_A9D398460EF3A604F9CB6EA1985EAA4A" xlink:type="locator" />
    <definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_A9D398460EF3A604F9CB6EA1985EAA4A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_AdverseLossReserveDevelopmentOnLossesOccurringInYears2000AndPrior" xlink:label="loc_ob_AdverseLossReserveDevelopmentOnLossesOccurringInYears2000AndPrior_ED31600123FC968401516E96634FC1C1" xlink:type="locator" />
    <definitionArc order="19" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_ob_AdverseLossReserveDevelopmentOnLossesOccurringInYears2000AndPrior_ED31600123FC968401516E96634FC1C1" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_LossReservesCededAtAcquisition" xlink:label="loc_ob_LossReservesCededAtAcquisition_676AD36C1A0C59A6AE106E96634FEAE1" xlink:type="locator" />
    <definitionArc order="20" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_ob_LossReservesCededAtAcquisition_676AD36C1A0C59A6AE106E96634FEAE1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForAsbestosAndEnvironmentalClaimsNet" xlink:label="loc_us-gaap_LiabilityForAsbestosAndEnvironmentalClaimsNet_E670EEA87493F1E012CC6E96634F60D0" xlink:type="locator" />
    <definitionArc order="21" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_LiabilityForAsbestosAndEnvironmentalClaimsNet_E670EEA87493F1E012CC6E96634F60D0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRecoverables" xlink:label="loc_us-gaap_ReinsuranceRecoverables_8EE9C32642D55D09C97F6E96634F6C35" xlink:type="locator" />
    <definitionArc order="22" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_ReinsuranceRecoverables_8EE9C32642D55D09C97F6E96634F6C35" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_LiabilitiesForAsbestosAndEnvironmentalClaimsEstimatedFutureLosses" xlink:label="loc_ob_LiabilitiesForAsbestosAndEnvironmentalClaimsEstimatedFutureLosses_445D4C984E7E430B35CF6E96634F32E1" xlink:type="locator" />
    <definitionArc order="23" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_ob_LiabilitiesForAsbestosAndEnvironmentalClaimsEstimatedFutureLosses_445D4C984E7E430B35CF6E96634F32E1" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_EstimatedIncurredLossesCeded" xlink:label="loc_ob_EstimatedIncurredLossesCeded_CD31A24E768903D492786E96634F1B44" xlink:type="locator" />
    <definitionArc order="24" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_ob_EstimatedIncurredLossesCeded_CD31A24E768903D492786E96634F1B44" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceReceivablesPaidLossesRecoverable" xlink:label="loc_us-gaap_ReinsuranceReceivablesPaidLossesRecoverable_4CC32F784CF8FBD58C126E96634FB14B" xlink:type="locator" />
    <definitionArc order="25" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_ReinsuranceReceivablesPaidLossesRecoverable_4CC32F784CF8FBD58C126E96634FB14B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRecoverablesPercentageOfTotal" xlink:label="loc_us-gaap_ReinsuranceRecoverablesPercentageOfTotal_62489378B39566A88C186E96634F4DCC" xlink:type="locator" />
    <definitionArc order="26" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_us-gaap_ReinsuranceRecoverablesPercentageOfTotal_62489378B39566A88C186E96634F4DCC" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_AmBestRatingSystemNumberOfRatings" xlink:label="loc_ob_AmBestRatingSystemNumberOfRatings_0A44D05A417B0015363C6E96634F9394" xlink:type="locator" />
    <definitionArc order="27" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_ob_AmBestRatingSystemNumberOfRatings_0A44D05A417B0015363C6E96634F9394" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ReinsuranceRecoverablesGuaranteed" xlink:label="loc_ob_ReinsuranceRecoverablesGuaranteed_3A9D147AFCD7F5EAE69E6E96634FD030" xlink:type="locator" />
    <definitionArc order="28" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C4E097D0F4815CBDBA736E96634F4C1B" xlink:to="loc_ob_ReinsuranceRecoverablesGuaranteed_3A9D147AFCD7F5EAE69E6E96634FD030" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/DiscontinuedOperationsLossPerShareRelatedToDiscontinuedOperationsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C2DDCB1671C179E7B2016E96698624F2" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_D266E6DB8969A72208EE6E966986D205" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C2DDCB1671C179E7B2016E96698624F2" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_D266E6DB8969A72208EE6E966986D205" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_DB3600D2272E5467A40A6E9669863068" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_D266E6DB8969A72208EE6E966986D205" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_DB3600D2272E5467A40A6E9669863068" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_10E9A99B6B2E60D9A77F6E966986DD1E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_DB3600D2272E5467A40A6E9669863068" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_10E9A99B6B2E60D9A77F6E966986DD1E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_10E9A99B6B2E60D9A77F6E966986DD1E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_DB3600D2272E5467A40A6E9669863068" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_10E9A99B6B2E60D9A77F6E966986DD1E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDiscontinuedOperationsMember" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_7AEAC44768739B03D3EF6E9669861BE8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_10E9A99B6B2E60D9A77F6E966986DD1E" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_7AEAC44768739B03D3EF6E9669861BE8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasicAndDilutedAbstract" xlink:label="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_1ABCEA218374737C2F6F6E966986D215" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C2DDCB1671C179E7B2016E96698624F2" xlink:to="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_1ABCEA218374737C2F6F6E966986D215" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_CA4380978C532858F97A6E966986CA47" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_1ABCEA218374737C2F6F6E966986D215" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_CA4380978C532858F97A6E966986CA47" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_IncomeLossAllocatedToParticipatingUnvestedRestrictedCommonShares" xlink:label="loc_ob_IncomeLossAllocatedToParticipatingUnvestedRestrictedCommonShares_169CB832B1ECF420BFDB6E966986481E" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_1ABCEA218374737C2F6F6E966986D215" xlink:to="loc_ob_IncomeLossAllocatedToParticipatingUnvestedRestrictedCommonShares_169CB832B1ECF420BFDB6E966986481E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_682A9C98AA8601602CC66E966986704E" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_1ABCEA218374737C2F6F6E966986D215" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_682A9C98AA8601602CC66E966986704E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_F146D454F1CEF430EE4D6E9DB50A8312" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C2DDCB1671C179E7B2016E96698624F2" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_F146D454F1CEF430EE4D6E9DB50A8312" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_350514F7544204760BCA6E966986F0CF" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C2DDCB1671C179E7B2016E96698624F2" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_350514F7544204760BCA6E966986F0CF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesIssuedBasic" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesIssuedBasic_7BADE8A01D1DB39E60D26E966986C9C1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_350514F7544204760BCA6E966986F0CF" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesIssuedBasic_7BADE8A01D1DB39E60D26E966986C9C1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesRestrictedStock" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesRestrictedStock_C20F0EE9CFDA12C952036E9669867D13" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_350514F7544204760BCA6E966986F0CF" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesRestrictedStock_C20F0EE9CFDA12C952036E9669867D13" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_EBBD218732654356D5D86E9669865EB2" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_350514F7544204760BCA6E966986F0CF" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_EBBD218732654356D5D86E9669865EB2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasicAbstract" xlink:label="loc_us-gaap_EarningsPerShareBasicAbstract_001B4C5874C863B115826E966986EDEA" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_C2DDCB1671C179E7B2016E96698624F2" xlink:to="loc_us-gaap_EarningsPerShareBasicAbstract_001B4C5874C863B115826E966986EDEA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasicAndDiluted" xlink:label="loc_us-gaap_EarningsPerShareBasicAndDiluted_B8B29D7259D3BF05D9036E9669864936" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_001B4C5874C863B115826E966986EDEA" xlink:to="loc_us-gaap_EarningsPerShareBasicAndDiluted_B8B29D7259D3BF05D9036E9669864936" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/DiscontinuedOperationsSummaryOfReclassifiedBalancesAndRelatedItemsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7E022472707E51C3E7466A79B05B8C9C" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_F3CD7BD4B520EDAE7A5E6A79B04B8587" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7E022472707E51C3E7466A79B05B8C9C" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_F3CD7BD4B520EDAE7A5E6A79B04B8587" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_F209E5DAEB6B9AF213896A79B04B7F97" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_F3CD7BD4B520EDAE7A5E6A79B04B8587" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_F209E5DAEB6B9AF213896A79B04B7F97" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_00BD2F6938DFB291D34E6A79B05BB5DA_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_F209E5DAEB6B9AF213896A79B04B7F97" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_00BD2F6938DFB291D34E6A79B05BB5DA_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_00BD2F6938DFB291D34E6A79B05BB5DA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_F209E5DAEB6B9AF213896A79B04B7F97" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_00BD2F6938DFB291D34E6A79B05BB5DA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDiscontinuedOperationsMember" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_7CD8A8E4B448B1360CDA6A79B05BC9D6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_00BD2F6938DFB291D34E6A79B05BB5DA" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_7CD8A8E4B448B1360CDA6A79B05BC9D6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_ED0069BD273ED4829A556A79B05B911F" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_F3CD7BD4B520EDAE7A5E6A79B04B8587" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_ED0069BD273ED4829A556A79B05B911F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_426FA05864F2855C50EF6A79B05B6F35_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_ED0069BD273ED4829A556A79B05B911F" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_426FA05864F2855C50EF6A79B05B6F35_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_426FA05864F2855C50EF6A79B05B6F35" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_ED0069BD273ED4829A556A79B05B911F" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_426FA05864F2855C50EF6A79B05B6F35" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RunoffMember" xlink:label="loc_ob_RunoffMember_AEB1A5AD71FB7B62AAA46A79B05BFD7A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_426FA05864F2855C50EF6A79B05B6F35" xlink:to="loc_ob_RunoffMember_AEB1A5AD71FB7B62AAA46A79B05BFD7A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRecoverablesGross" xlink:label="loc_us-gaap_ReinsuranceRecoverablesGross_D531A17BAE9C9FC167576A79B05BF4F3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7E022472707E51C3E7466A79B05B8C9C" xlink:to="loc_us-gaap_ReinsuranceRecoverablesGross_D531A17BAE9C9FC167576A79B05BF4F3" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_QuotaShareReinsuranceAgreementPercentage" xlink:label="loc_ob_QuotaShareReinsuranceAgreementPercentage_A667263B0626DA9526026A79B05B26F3" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7E022472707E51C3E7466A79B05B8C9C" xlink:to="loc_ob_QuotaShareReinsuranceAgreementPercentage_A667263B0626DA9526026A79B05B26F3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_1BBCDE5A46058E7D1A866A79B05B0832" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7E022472707E51C3E7466A79B05B8C9C" xlink:to="loc_us-gaap_AssetsAbstract_1BBCDE5A46058E7D1A866A79B05B0832" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Investments" xlink:label="loc_us-gaap_Investments_67823DA71704580EB2C26A79B05B08E7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_1BBCDE5A46058E7D1A866A79B05B0832" xlink:to="loc_us-gaap_Investments_67823DA71704580EB2C26A79B05B08E7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PremiumsReceivableAtCarryingValue" xlink:label="loc_us-gaap_PremiumsReceivableAtCarryingValue_609E5A30F4C5623CA13A6A79B05B88A7" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_1BBCDE5A46058E7D1A866A79B05B0832" xlink:to="loc_us-gaap_PremiumsReceivableAtCarryingValue_609E5A30F4C5623CA13A6A79B05B88A7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims" xlink:label="loc_us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims_F791F3ABCA7FAC877CC06A79B05B4697" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_1BBCDE5A46058E7D1A866A79B05B0832" xlink:to="loc_us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims_F791F3ABCA7FAC877CC06A79B05B4697" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceReceivablesPaidLossesRecoverable" xlink:label="loc_us-gaap_ReinsuranceReceivablesPaidLossesRecoverable_E9AE975DEC13F98890CB6A79B05B828D" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_1BBCDE5A46058E7D1A866A79B05B0832" xlink:to="loc_us-gaap_ReinsuranceReceivablesPaidLossesRecoverable_E9AE975DEC13F98890CB6A79B05B828D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsNet" xlink:label="loc_us-gaap_DeferredTaxAssetsNet_B4A42C8E4AD51997CE5F6A79B05BEDF9" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_1BBCDE5A46058E7D1A866A79B05B0832" xlink:to="loc_us-gaap_DeferredTaxAssetsNet_B4A42C8E4AD51997CE5F6A79B05BEDF9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherAssets" xlink:label="loc_us-gaap_OtherAssets_8858F273CBD39E472C0B6A79B05B9F9D" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_1BBCDE5A46058E7D1A866A79B05B0832" xlink:to="loc_us-gaap_OtherAssets_8858F273CBD39E472C0B6A79B05B9F9D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_C19E79BAFECE468678E86A79B05BF3CA" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_1BBCDE5A46058E7D1A866A79B05B0832" xlink:to="loc_us-gaap_Assets_C19E79BAFECE468678E86A79B05BF3CA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesAbstract" xlink:label="loc_us-gaap_LiabilitiesAbstract_F65048469825DD54C74D6A79B05BE738" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7E022472707E51C3E7466A79B05B8C9C" xlink:to="loc_us-gaap_LiabilitiesAbstract_F65048469825DD54C74D6A79B05BE738" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_D391E573E3C494EF12276A79B05BCB4C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_F65048469825DD54C74D6A79B05BE738" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_D391E573E3C494EF12276A79B05BCB4C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_UnearnedPremiums" xlink:label="loc_us-gaap_UnearnedPremiums_9E92EAD69F3B6845032F6A79B05BA932" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_F65048469825DD54C74D6A79B05BE738" xlink:to="loc_us-gaap_UnearnedPremiums_9E92EAD69F3B6845032F6A79B05BA932" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsurancePayable" xlink:label="loc_us-gaap_ReinsurancePayable_A155A6563C31C4E816C46A79B05B2A33" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_F65048469825DD54C74D6A79B05BE738" xlink:to="loc_us-gaap_ReinsurancePayable_A155A6563C31C4E816C46A79B05B2A33" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLiabilities" xlink:label="loc_us-gaap_OtherLiabilities_6206095D417B3259B2756A79B05B9DE8" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_F65048469825DD54C74D6A79B05BE738" xlink:to="loc_us-gaap_OtherLiabilities_6206095D417B3259B2756A79B05B9DE8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Liabilities" xlink:label="loc_us-gaap_Liabilities_2F8830BF1DB896F74E616A79B05B55DF" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_F65048469825DD54C74D6A79B05BE738" xlink:to="loc_us-gaap_Liabilities_2F8830BF1DB896F74E616A79B05B55DF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_992BEC3BDDF1733EAAC36A79B05BFC51" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_7E022472707E51C3E7466A79B05B8C9C" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_992BEC3BDDF1733EAAC36A79B05BFC51" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/DiscontinuedOperationsSummaryOfResultsOfOperationsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_9AF4735E94E8DE74D0DD69FD0D790004" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_604D0A75683D9983181F69FD0D79AF3C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_9AF4735E94E8DE74D0DD69FD0D790004" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_604D0A75683D9983181F69FD0D79AF3C" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_189D4E90D62490E4FC0B69FD0D790C0D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_604D0A75683D9983181F69FD0D79AF3C" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_189D4E90D62490E4FC0B69FD0D790C0D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_46142C1DB986EF44FAD969FD0D79FAB5_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_189D4E90D62490E4FC0B69FD0D790C0D" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_46142C1DB986EF44FAD969FD0D79FAB5_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_46142C1DB986EF44FAD969FD0D79FAB5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_189D4E90D62490E4FC0B69FD0D790C0D" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_46142C1DB986EF44FAD969FD0D79FAB5" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RunoffMember" xlink:label="loc_ob_RunoffMember_CD78FE1F75F7905523CF69FD0D79C407" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_46142C1DB986EF44FAD969FD0D79FAB5" xlink:to="loc_ob_RunoffMember_CD78FE1F75F7905523CF69FD0D79C407" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_478A55D5F0137CB8912669FD0D79A316" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_604D0A75683D9983181F69FD0D79AF3C" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_478A55D5F0137CB8912669FD0D79A316" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_F71A4EEDA17901DB2B6669FD0D798551_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_478A55D5F0137CB8912669FD0D79A316" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_F71A4EEDA17901DB2B6669FD0D798551_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_F71A4EEDA17901DB2B6669FD0D798551" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_478A55D5F0137CB8912669FD0D79A316" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_F71A4EEDA17901DB2B6669FD0D798551" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDiscontinuedOperationsMember" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_2584A1069842E743D9BF69FD0D79AA46" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_F71A4EEDA17901DB2B6669FD0D798551" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_2584A1069842E743D9BF69FD0D79AA46" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PremiumsWrittenNet" xlink:label="loc_us-gaap_PremiumsWrittenNet_D233D587F1CE1F6050ED69FD0D7941E7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_9AF4735E94E8DE74D0DD69FD0D790004" xlink:to="loc_us-gaap_PremiumsWrittenNet_D233D587F1CE1F6050ED69FD0D7941E7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RevenuesAbstract" xlink:label="loc_us-gaap_RevenuesAbstract_B190B6661217FF779D1A69FD0D7986BD" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_9AF4735E94E8DE74D0DD69FD0D790004" xlink:to="loc_us-gaap_RevenuesAbstract_B190B6661217FF779D1A69FD0D7986BD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PremiumsEarnedNet" xlink:label="loc_us-gaap_PremiumsEarnedNet_2163EA4716295D8CB61A69FD0D7A5FDC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_B190B6661217FF779D1A69FD0D7986BD" xlink:to="loc_us-gaap_PremiumsEarnedNet_2163EA4716295D8CB61A69FD0D7A5FDC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherIncome" xlink:label="loc_us-gaap_OtherIncome_B403D4A6F016E34592E96A5743EA0E74" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_B190B6661217FF779D1A69FD0D7986BD" xlink:to="loc_us-gaap_OtherIncome_B403D4A6F016E34592E96A5743EA0E74" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_4CC8F7D2A160225DFE1369FD0D7A371D" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_B190B6661217FF779D1A69FD0D7986BD" xlink:to="loc_us-gaap_Revenues_4CC8F7D2A160225DFE1369FD0D7A371D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BenefitsLossesAndExpensesAbstract" xlink:label="loc_us-gaap_BenefitsLossesAndExpensesAbstract_357363F33AE4C516218269FD0D7A231B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_9AF4735E94E8DE74D0DD69FD0D790004" xlink:to="loc_us-gaap_BenefitsLossesAndExpensesAbstract_357363F33AE4C516218269FD0D7A231B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PolicyholderBenefitsAndClaimsIncurredNet" xlink:label="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_AD4AF88C1B6142CD006269FD0D7A8665" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BenefitsLossesAndExpensesAbstract_357363F33AE4C516218269FD0D7A231B" xlink:to="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_AD4AF88C1B6142CD006269FD0D7A8665" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_DisposalGroupIncludingDiscontinuedOperationUnderwritingExpensesNetOfTax" xlink:label="loc_ob_DisposalGroupIncludingDiscontinuedOperationUnderwritingExpensesNetOfTax_3FA4935ABBD3FC55E96969FD0D7A8598" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BenefitsLossesAndExpensesAbstract_357363F33AE4C516218269FD0D7A231B" xlink:to="loc_ob_DisposalGroupIncludingDiscontinuedOperationUnderwritingExpensesNetOfTax_3FA4935ABBD3FC55E96969FD0D7A8598" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InsuranceAndReinsuranceAcquisitionExpenses" xlink:label="loc_ob_InsuranceAndReinsuranceAcquisitionExpenses_D65E8C23264F3277701C69FD0D7AD0F7" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BenefitsLossesAndExpensesAbstract_357363F33AE4C516218269FD0D7A231B" xlink:to="loc_ob_InsuranceAndReinsuranceAcquisitionExpenses_D65E8C23264F3277701C69FD0D7AD0F7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BenefitsLossesAndExpenses" xlink:label="loc_us-gaap_BenefitsLossesAndExpenses_2510D476FC5B4BD7693E69FD0D7AE855" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BenefitsLossesAndExpensesAbstract_357363F33AE4C516218269FD0D7A231B" xlink:to="loc_us-gaap_BenefitsLossesAndExpenses_2510D476FC5B4BD7693E69FD0D7AE855" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_951CE51994FD3229550869FD0D7AE68E" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_9AF4735E94E8DE74D0DD69FD0D790004" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_951CE51994FD3229550869FD0D7AE68E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_B3430F59F74BB154870269FD0D7AF9E2" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_9AF4735E94E8DE74D0DD69FD0D790004" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_B3430F59F74BB154870269FD0D7AF9E2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_B26652E262055E33AB0269FD0D7A6456" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_9AF4735E94E8DE74D0DD69FD0D790004" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax_B26652E262055E33AB0269FD0D7A6456" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_6F66A53D184F8BB4B6C369FD0D7A9965" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_9AF4735E94E8DE74D0DD69FD0D790004" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_6F66A53D184F8BB4B6C369FD0D7A9965" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_CAA95D0C3CE5F76101EF6A5749DC5FED" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_9AF4735E94E8DE74D0DD69FD0D790004" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_CAA95D0C3CE5F76101EF6A5749DC5FED" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/DiscontinuedOperationsTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/DocumentAndEntityInformation" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="loc_us-gaap_StatementTable_4900E1FBC1D5DE94823AFCADA89E97D0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:to="loc_us-gaap_StatementTable_4900E1FBC1D5DE94823AFCADA89E97D0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="loc_us-gaap_StatementClassOfStockAxis_F86F90D3335EE63D7EE2FCADA89EF4E9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_4900E1FBC1D5DE94823AFCADA89E97D0" xlink:to="loc_us-gaap_StatementClassOfStockAxis_F86F90D3335EE63D7EE2FCADA89EF4E9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_19C44292331EA3B179C5FCADA89E873D_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_F86F90D3335EE63D7EE2FCADA89EF4E9" xlink:to="loc_us-gaap_ClassOfStockDomain_19C44292331EA3B179C5FCADA89E873D_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="loc_us-gaap_ClassOfStockDomain_19C44292331EA3B179C5FCADA89E873D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_F86F90D3335EE63D7EE2FCADA89EF4E9" xlink:to="loc_us-gaap_ClassOfStockDomain_19C44292331EA3B179C5FCADA89E873D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonClassAMember" xlink:label="loc_us-gaap_CommonClassAMember_C211B8857BBB70478551FCADA89EF9AD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_19C44292331EA3B179C5FCADA89E873D" xlink:to="loc_us-gaap_CommonClassAMember_C211B8857BBB70478551FCADA89EF9AD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonClassBMember" xlink:label="loc_us-gaap_CommonClassBMember_F690B0A67C9EA92A33C5FCADA89E80FB" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_19C44292331EA3B179C5FCADA89E873D" xlink:to="loc_us-gaap_CommonClassBMember_F690B0A67C9EA92A33C5FCADA89E80FB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityRegistrantName" xlink:label="loc_dei_EntityRegistrantName_09D17D1D582CDE513B54FCADA89E1923" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:to="loc_dei_EntityRegistrantName_09D17D1D582CDE513B54FCADA89E1923" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="loc_dei_EntityCentralIndexKey_D4A90C89ACB23644C710FCADA89E7D20" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:to="loc_dei_EntityCentralIndexKey_D4A90C89ACB23644C710FCADA89E7D20" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentType" xlink:label="loc_dei_DocumentType_A389C560FDE7689E81E4FCADA89E0199" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:to="loc_dei_DocumentType_A389C560FDE7689E81E4FCADA89E0199" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="loc_dei_DocumentPeriodEndDate_C8C30B311AA06F628D9CFCADA89EE607" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:to="loc_dei_DocumentPeriodEndDate_C8C30B311AA06F628D9CFCADA89EE607" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_AmendmentFlag" xlink:label="loc_dei_AmendmentFlag_1B001F9C35C1F9A6DF7BFCADA89E9076" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:to="loc_dei_AmendmentFlag_1B001F9C35C1F9A6DF7BFCADA89E9076" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:label="loc_dei_CurrentFiscalYearEndDate_E0711231D03994D5C07DFCADA89E20A6" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:to="loc_dei_CurrentFiscalYearEndDate_E0711231D03994D5C07DFCADA89E20A6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityFilerCategory" xlink:label="loc_dei_EntityFilerCategory_C63F138D6427CD136BACFCADA89E3B77" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:to="loc_dei_EntityFilerCategory_C63F138D6427CD136BACFCADA89E3B77" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_C8B70571329AB2F2402DFCADA89EAA4E" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_C8B70571329AB2F2402DFCADA89EAA4E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:label="loc_dei_DocumentFiscalYearFocus_FEBDECEFB46C7CFCB598FCADA89EB0E2" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:to="loc_dei_DocumentFiscalYearFocus_FEBDECEFB46C7CFCB598FCADA89EB0E2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="loc_dei_DocumentFiscalPeriodFocus_8C0897F03DEC667980B1FCADA89EF06D" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_DE702CB32E51181BF01BFCADA89E74C0" xlink:to="loc_dei_DocumentFiscalPeriodFocus_8C0897F03DEC667980B1FCADA89EF06D" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/EarningsPerShare" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/EarningsPerShareDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasicLineItems" xlink:label="loc_us-gaap_EarningsPerShareBasicLineItems_79212601929303711D556A9445ED28DA" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable" xlink:label="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_EA76D597794EC5D85A9D6A94455D92E1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_79212601929303711D556A9445ED28DA" xlink:to="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_EA76D597794EC5D85A9D6A94455D92E1" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_9915A5F6DF6474AC673869FD0D94574A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_EA76D597794EC5D85A9D6A94455D92E1" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_9915A5F6DF6474AC673869FD0D94574A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_D3205214FF03BAAE6C6669FD0D9498C0_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_9915A5F6DF6474AC673869FD0D94574A" xlink:to="loc_us-gaap_EquityComponentDomain_D3205214FF03BAAE6C6669FD0D9498C0_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_D3205214FF03BAAE6C6669FD0D9498C0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_9915A5F6DF6474AC673869FD0D94574A" xlink:to="loc_us-gaap_EquityComponentDomain_D3205214FF03BAAE6C6669FD0D9498C0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ParentMember" xlink:label="loc_us-gaap_ParentMember_B5A4FDFDFD7D414FCF2B69FD0D946759" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_D3205214FF03BAAE6C6669FD0D9498C0" xlink:to="loc_us-gaap_ParentMember_B5A4FDFDFD7D414FCF2B69FD0D946759" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasicAndDilutedAbstract" xlink:label="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_EFBCFF36FC3794FC2ACB69FD0D9447B0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_79212601929303711D556A9445ED28DA" xlink:to="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_EFBCFF36FC3794FC2ACB69FD0D9447B0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperations" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperations_4005D206914E59C547BE69FD0D948205" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_EFBCFF36FC3794FC2ACB69FD0D9447B0" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperations_4005D206914E59C547BE69FD0D948205" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_IncomeLossAllocatedToParticipatingUnvestedRestrictedCommonShares" xlink:label="loc_ob_IncomeLossAllocatedToParticipatingUnvestedRestrictedCommonShares_67842677F2078CAE2A5069FD0D941BCF" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_EFBCFF36FC3794FC2ACB69FD0D9447B0" xlink:to="loc_ob_IncomeLossAllocatedToParticipatingUnvestedRestrictedCommonShares_67842677F2078CAE2A5069FD0D941BCF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DividendsShareBasedCompensation" xlink:label="loc_us-gaap_DividendsShareBasedCompensation_6C12611F40A33DE363FD69FD0D9494CD" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_EFBCFF36FC3794FC2ACB69FD0D9447B0" xlink:to="loc_us-gaap_DividendsShareBasedCompensation_6C12611F40A33DE363FD69FD0D9494CD" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_AggregateAllocationToRestrictedSharesIncludingDividend" xlink:label="loc_ob_AggregateAllocationToRestrictedSharesIncludingDividend_B73698238A05DAF0C2C269FD0D94A0BE" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_EFBCFF36FC3794FC2ACB69FD0D9447B0" xlink:to="loc_ob_AggregateAllocationToRestrictedSharesIncludingDividend_B73698238A05DAF0C2C269FD0D94A0BE" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_IncomeLossFromContinuingOperatingsExcludingPortionAttributableToNoncontrollingInterestNet" xlink:label="loc_ob_IncomeLossFromContinuingOperatingsExcludingPortionAttributableToNoncontrollingInterestNet_D6E7E15D8FE73D690BD169FD0D943AFA" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_EFBCFF36FC3794FC2ACB69FD0D9447B0" xlink:to="loc_ob_IncomeLossFromContinuingOperatingsExcludingPortionAttributableToNoncontrollingInterestNet_D6E7E15D8FE73D690BD169FD0D943AFA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_UndistributedEarningsAbstract" xlink:label="loc_us-gaap_UndistributedEarningsAbstract_99AB499BE62ECC67874C69FD0D94ADDC" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_79212601929303711D556A9445ED28DA" xlink:to="loc_us-gaap_UndistributedEarningsAbstract_99AB499BE62ECC67874C69FD0D94ADDC" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_DividendsCommonStockCashNetOfRestrictedCommonShareAmounts" xlink:label="loc_ob_DividendsCommonStockCashNetOfRestrictedCommonShareAmounts_D42FFA253604428B8FD069FD0D94E5C3" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UndistributedEarningsAbstract_99AB499BE62ECC67874C69FD0D94ADDC" xlink:to="loc_ob_DividendsCommonStockCashNetOfRestrictedCommonShareAmounts_D42FFA253604428B8FD069FD0D94E5C3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_UndistributedEarnings" xlink:label="loc_us-gaap_UndistributedEarnings_06D6E491AFD14C113C5869FD0D954470" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UndistributedEarningsAbstract_99AB499BE62ECC67874C69FD0D94ADDC" xlink:to="loc_us-gaap_UndistributedEarnings_06D6E491AFD14C113C5869FD0D954470" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_4971D755B6E445D3DCFF69FD0D95B195" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_79212601929303711D556A9445ED28DA" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_4971D755B6E445D3DCFF69FD0D95B195" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesIssuedBasic" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesIssuedBasic_85D21600EF5F93126C6269FD0D95BC92" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_4971D755B6E445D3DCFF69FD0D95B195" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesIssuedBasic_85D21600EF5F93126C6269FD0D95BC92" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesRestrictedStock" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesRestrictedStock_B97B566A654A2AEDCB4369FD0D95AA75" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_4971D755B6E445D3DCFF69FD0D95B195" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesRestrictedStock_B97B566A654A2AEDCB4369FD0D95AA75" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_76D9D83C2762F1D2ADF769FD0D9557A1" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_4971D755B6E445D3DCFF69FD0D95B195" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_76D9D83C2762F1D2ADF769FD0D9557A1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasicAndDilutedOtherDisclosuresAbstract" xlink:label="loc_us-gaap_EarningsPerShareBasicAndDilutedOtherDisclosuresAbstract_7DBBF2B00BD613AD5C1869FD0D95E1B0" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_79212601929303711D556A9445ED28DA" xlink:to="loc_us-gaap_EarningsPerShareBasicAndDilutedOtherDisclosuresAbstract_7DBBF2B00BD613AD5C1869FD0D95E1B0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsPerBasicShare" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_5F070CB08C894131418A69FD0D9529A5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedOtherDisclosuresAbstract_7DBBF2B00BD613AD5C1869FD0D95E1B0" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_5F070CB08C894131418A69FD0D9529A5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockDividendsPerShareCashPaid" xlink:label="loc_us-gaap_CommonStockDividendsPerShareCashPaid_9E7890E9D2907960342F69FD0D957893" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedOtherDisclosuresAbstract_7DBBF2B00BD613AD5C1869FD0D95E1B0" xlink:to="loc_us-gaap_CommonStockDividendsPerShareCashPaid_9E7890E9D2907960342F69FD0D957893" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasicUndistributed" xlink:label="loc_us-gaap_EarningsPerShareBasicUndistributed_80A1951504B0A372703969FD0D95B891" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedOtherDisclosuresAbstract_7DBBF2B00BD613AD5C1869FD0D95E1B0" xlink:to="loc_us-gaap_EarningsPerShareBasicUndistributed_80A1951504B0A372703969FD0D95B891" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/EarningsPerShareTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/EmployeeShareBasedIncentiveCompensationPlans" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/EmployeeShareBasedIncentiveCompensationPlansEmployeeShareBasedCompensationPlansDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/EmployeeShareBasedIncentiveCompensationPlansPerformanceSharesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ADCD3A4A110DC59A977401839E6732E1" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BD942E293E70F662B60401839E586E11" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ADCD3A4A110DC59A977401839E6732E1" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BD942E293E70F662B60401839E586E11" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_2ADE226814646006D39701839E67616A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BD942E293E70F662B60401839E586E11" xlink:to="loc_us-gaap_PlanNameAxis_2ADE226814646006D39701839E67616A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_F6C0A6D23844779B370D01839E671FA7_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_2ADE226814646006D39701839E67616A" xlink:to="loc_us-gaap_PlanNameDomain_F6C0A6D23844779B370D01839E671FA7_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_F6C0A6D23844779B370D01839E671FA7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_2ADE226814646006D39701839E67616A" xlink:to="loc_us-gaap_PlanNameDomain_F6C0A6D23844779B370D01839E671FA7" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_LongTermIncentivePlanMember" xlink:label="loc_ob_LongTermIncentivePlanMember_AC90C61818D5701C10C201839E676F79" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_F6C0A6D23844779B370D01839E671FA7" xlink:to="loc_ob_LongTermIncentivePlanMember_AC90C61818D5701C10C201839E676F79" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_E6F2AE57DD6D70670B3701839E67D24E" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BD942E293E70F662B60401839E586E11" xlink:to="loc_us-gaap_AwardTypeAxis_E6F2AE57DD6D70670B3701839E67D24E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1E389241C151E558A76701839E676409_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_E6F2AE57DD6D70670B3701839E67D24E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1E389241C151E558A76701839E676409_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1E389241C151E558A76701839E676409" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_E6F2AE57DD6D70670B3701839E67D24E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1E389241C151E558A76701839E676409" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PerformanceSharesMember" xlink:label="loc_us-gaap_PerformanceSharesMember_1C87306C8D10D0D8153601839E67E73D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1E389241C151E558A76701839E676409" xlink:to="loc_us-gaap_PerformanceSharesMember_1C87306C8D10D0D8153601839E67E73D" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleAxis" xlink:label="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleAxis_18590A1C6E3AA2588E4801839E67C547" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_BD942E293E70F662B60401839E586E11" xlink:to="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleAxis_18590A1C6E3AA2588E4801839E67C547" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain" xlink:label="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain_68AF0EC3A4B87F43965E01839E672457_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleAxis_18590A1C6E3AA2588E4801839E67C547" xlink:to="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain_68AF0EC3A4B87F43965E01839E672457_default" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain" xlink:label="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain_68AF0EC3A4B87F43965E01839E672457" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleAxis_18590A1C6E3AA2588E4801839E67C547" xlink:to="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain_68AF0EC3A4B87F43965E01839E672457" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RangeOfPerformanceCycleFrom2011To2013Member" xlink:label="loc_ob_RangeOfPerformanceCycleFrom2011To2013Member_8AEBF6272C04131BD04401839E675FD8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain_68AF0EC3A4B87F43965E01839E672457" xlink:to="loc_ob_RangeOfPerformanceCycleFrom2011To2013Member_8AEBF6272C04131BD04401839E675FD8" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RangeOfPerformanceCycleFrom2012To2014Member" xlink:label="loc_ob_RangeOfPerformanceCycleFrom2012To2014Member_02903A9A4C6FBB3F1F6601839E67BE31" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain_68AF0EC3A4B87F43965E01839E672457" xlink:to="loc_ob_RangeOfPerformanceCycleFrom2012To2014Member_02903A9A4C6FBB3F1F6601839E67BE31" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RangeOfPerformanceCycleFrom2013To2015Member" xlink:label="loc_ob_RangeOfPerformanceCycleFrom2013To2015Member_3F9E1B7D75040366EE6901839E67E695" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain_68AF0EC3A4B87F43965E01839E672457" xlink:to="loc_ob_RangeOfPerformanceCycleFrom2013To2015Member_3F9E1B7D75040366EE6901839E67E695" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RangeofPerformanceCyclefrom2014To2016Member" xlink:label="loc_ob_RangeofPerformanceCyclefrom2014To2016Member_C0EFE4534EED48263B9001839E67EF16" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain_68AF0EC3A4B87F43965E01839E672457" xlink:to="loc_ob_RangeofPerformanceCyclefrom2014To2016Member_C0EFE4534EED48263B9001839E67EF16" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PerformanceCycle20122016Member" xlink:label="loc_ob_PerformanceCycle20122016Member_6131D2CE40278100224701839E676AD5" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain_68AF0EC3A4B87F43965E01839E672457" xlink:to="loc_ob_PerformanceCycle20122016Member_6131D2CE40278100224701839E676AD5" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RangeOfPerformanceCycleFrom2010To2012Member" xlink:label="loc_ob_RangeOfPerformanceCycleFrom2010To2012Member_C1F6CE609C074ACAD31A01839E67E342" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_ShareBasedCompensationArrangementByPerformanceSharesAwardPerformanceCycleDomain_68AF0EC3A4B87F43965E01839E672457" xlink:to="loc_ob_RangeOfPerformanceCycleFrom2010To2012Member_C1F6CE609C074ACAD31A01839E67E342" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_908578353EFB7B2B04FE01839E6728C1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ADCD3A4A110DC59A977401839E6732E1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_908578353EFB7B2B04FE01839E6728C1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_AE7B8EB5A845F1163A7701839E67377A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_908578353EFB7B2B04FE01839E6728C1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_AE7B8EB5A845F1163A7701839E67377A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsTargetSharesPaidInPeriod" xlink:label="loc_ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsTargetSharesPaidInPeriod_4DD2AF987FDC138AFEDF01839E67599C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_908578353EFB7B2B04FE01839E6728C1" xlink:to="loc_ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsTargetSharesPaidInPeriod_4DD2AF987FDC138AFEDF01839E67599C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_381D2D3C0A4A5176F9BA01839E67CA9F" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_908578353EFB7B2B04FE01839E6728C1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_381D2D3C0A4A5176F9BA01839E67CA9F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_AD81F32669D89378343901839E6758E5" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_908578353EFB7B2B04FE01839E6728C1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_AD81F32669D89378343901839E6758E5" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_AccruedExpenseRollForwardAbstract" xlink:label="loc_ob_AccruedExpenseRollForwardAbstract_640794BFD32A4B5EF20401839E678936" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ADCD3A4A110DC59A977401839E6732E1" xlink:to="loc_ob_AccruedExpenseRollForwardAbstract_640794BFD32A4B5EF20401839E678936" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_IncentiveCompensationPayable" xlink:label="loc_ob_IncentiveCompensationPayable_B2037023BABD32AC0E7101839E671E6F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_AccruedExpenseRollForwardAbstract_640794BFD32A4B5EF20401839E678936" xlink:to="loc_ob_IncentiveCompensationPayable_B2037023BABD32AC0E7101839E671E6F" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAmountsPaidInPeriod" xlink:label="loc_ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAmountsPaidInPeriod_161C05BE50B7EB4D115501839E67248D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_AccruedExpenseRollForwardAbstract_640794BFD32A4B5EF20401839E678936" xlink:to="loc_ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAmountsPaidInPeriod_161C05BE50B7EB4D115501839E67248D" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_EmployeeServiceShareBasedCompensationNonvestedAwardsForfeitedInPeriodTotalCompensationCostNotYetRecognized" xlink:label="loc_ob_EmployeeServiceShareBasedCompensationNonvestedAwardsForfeitedInPeriodTotalCompensationCostNotYetRecognized_47E3156F2BED7BBE3EBB01839E672E4E" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_AccruedExpenseRollForwardAbstract_640794BFD32A4B5EF20401839E678936" xlink:to="loc_ob_EmployeeServiceShareBasedCompensationNonvestedAwardsForfeitedInPeriodTotalCompensationCostNotYetRecognized_47E3156F2BED7BBE3EBB01839E672E4E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_E8CC31759C2BC336291E01839E67E4B3" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_AccruedExpenseRollForwardAbstract_640794BFD32A4B5EF20401839E678936" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_E8CC31759C2BC336291E01839E67E4B3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract_A52A6692793F21C84FD901839E67D780" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ADCD3A4A110DC59A977401839E6732E1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract_A52A6692793F21C84FD901839E67D780" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SharebasedCompensationArrangementbySharebasedPaymentAwardPayoutforMinimumGrowthTargetPercentage" xlink:label="loc_ob_SharebasedCompensationArrangementbySharebasedPaymentAwardPayoutforMinimumGrowthTargetPercentage_DA08F428A655B68E7C6C01839E675B7D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract_A52A6692793F21C84FD901839E67D780" xlink:to="loc_ob_SharebasedCompensationArrangementbySharebasedPaymentAwardPayoutforMinimumGrowthTargetPercentage_DA08F428A655B68E7C6C01839E675B7D" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumberBeforeForfeitures" xlink:label="loc_ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumberBeforeForfeitures_DC680D54DCDFEBDB0C0701839E679AAF" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract_A52A6692793F21C84FD901839E67D780" xlink:to="loc_ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumberBeforeForfeitures_DC680D54DCDFEBDB0C0701839E679AAF" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAssumedForfeituresInPeriod" xlink:label="loc_ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAssumedForfeituresInPeriod_489CF446297739C6927601839E67991C" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract_A52A6692793F21C84FD901839E67D780" xlink:to="loc_ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAssumedForfeituresInPeriod_489CF446297739C6927601839E67991C" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ShareBasedCompensationArrangementbyShareBasedPaymentAwardEquityInstrumentsOtherthanOptionsAssumedForfeituresPayable" xlink:label="loc_ob_ShareBasedCompensationArrangementbyShareBasedPaymentAwardEquityInstrumentsOtherthanOptionsAssumedForfeituresPayable_6E3F230956CA15AF7ACD01839E67AFE1" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract_A52A6692793F21C84FD901839E67D780" xlink:to="loc_ob_ShareBasedCompensationArrangementbyShareBasedPaymentAwardEquityInstrumentsOtherthanOptionsAssumedForfeituresPayable_6E3F230956CA15AF7ACD01839E67AFE1" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalCostToBeRecognizedIfPerformanceSharesVested" xlink:label="loc_ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalCostToBeRecognizedIfPerformanceSharesVested_89BD6A15D5159C40786D01839E674390" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalGeneralDisclosuresAbstract_A52A6692793F21C84FD901839E67D780" xlink:to="loc_ob_ShareBasedCompensationArrangementByShareBasedPaymentAwardAdditionalCostToBeRecognizedIfPerformanceSharesVested_89BD6A15D5159C40786D01839E674390" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/EmployeeShareBasedIncentiveCompensationPlansRestrictedDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BBCC4D405B279D6E320901839C160C5D" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FBD377073BF6E3FDA6D901839C0788A5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BBCC4D405B279D6E320901839C160C5D" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FBD377073BF6E3FDA6D901839C0788A5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TitleOfIndividualAxis" xlink:label="loc_us-gaap_TitleOfIndividualAxis_9CE037C179D5D6DB182501839C071FF8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FBD377073BF6E3FDA6D901839C0788A5" xlink:to="loc_us-gaap_TitleOfIndividualAxis_9CE037C179D5D6DB182501839C071FF8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_E02C4FC2002EC377EAE501839C0727C1_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TitleOfIndividualAxis_9CE037C179D5D6DB182501839C071FF8" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_E02C4FC2002EC377EAE501839C0727C1_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_E02C4FC2002EC377EAE501839C0727C1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TitleOfIndividualAxis_9CE037C179D5D6DB182501839C071FF8" xlink:to="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_E02C4FC2002EC377EAE501839C0727C1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ChiefExecutiveOfficerMember" xlink:label="loc_us-gaap_ChiefExecutiveOfficerMember_F7FCE50E365219E93A2F01839C1659C9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TitleOfIndividualWithRelationshipToEntityDomain_E02C4FC2002EC377EAE501839C0727C1" xlink:to="loc_us-gaap_ChiefExecutiveOfficerMember_F7FCE50E365219E93A2F01839C1659C9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardDateAxis" xlink:label="loc_us-gaap_AwardDateAxis_EFD1CA4B392F7FA26CA501839C16AFE0" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FBD377073BF6E3FDA6D901839C0788A5" xlink:to="loc_us-gaap_AwardDateAxis_EFD1CA4B392F7FA26CA501839C16AFE0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardDateDomain" xlink:label="loc_us-gaap_AwardDateDomain_4FFA0C3B6353F91BC0F601839C1675C8_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardDateAxis_EFD1CA4B392F7FA26CA501839C16AFE0" xlink:to="loc_us-gaap_AwardDateDomain_4FFA0C3B6353F91BC0F601839C1675C8_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardDateDomain" xlink:label="loc_us-gaap_AwardDateDomain_4FFA0C3B6353F91BC0F601839C1675C8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardDateAxis_EFD1CA4B392F7FA26CA501839C16AFE0" xlink:to="loc_us-gaap_AwardDateDomain_4FFA0C3B6353F91BC0F601839C1675C8" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_AwardsIssuedin2012Member" xlink:label="loc_ob_AwardsIssuedin2012Member_C14CC599CDC9BA46D57F01839C1643AF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AwardDateDomain_4FFA0C3B6353F91BC0F601839C1675C8" xlink:to="loc_ob_AwardsIssuedin2012Member_C14CC599CDC9BA46D57F01839C1643AF" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_AwardsIssuedin2011Member" xlink:label="loc_ob_AwardsIssuedin2011Member_9F7906A43F3BE681EB1001839C16F799" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AwardDateDomain_4FFA0C3B6353F91BC0F601839C1675C8" xlink:to="loc_ob_AwardsIssuedin2011Member_9F7906A43F3BE681EB1001839C16F799" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_F4F3F9595BEC86F98A3601839C160A0A" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_FBD377073BF6E3FDA6D901839C0788A5" xlink:to="loc_us-gaap_AwardTypeAxis_F4F3F9595BEC86F98A3601839C160A0A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_89BAC363C0E1939D327E01839C16BEDB_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_F4F3F9595BEC86F98A3601839C160A0A" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_89BAC363C0E1939D327E01839C16BEDB_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_89BAC363C0E1939D327E01839C16BEDB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_F4F3F9595BEC86F98A3601839C160A0A" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_89BAC363C0E1939D327E01839C16BEDB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_E494317E11E09C15FC0C01839C163C3C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_89BAC363C0E1939D327E01839C16BEDB" xlink:to="loc_us-gaap_RestrictedStockMember_E494317E11E09C15FC0C01839C163C3C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms_F08FA55BD87380604A6F01839C1614A6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BBCC4D405B279D6E320901839C160C5D" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms_F08FA55BD87380604A6F01839C1614A6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueVested" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueVested_F7B5F8624C150F0C024101839C1684F1" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BBCC4D405B279D6E320901839C160C5D" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueVested_F7B5F8624C150F0C024101839C1684F1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_FB1D717D8D05994FC04A01839C16220E" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BBCC4D405B279D6E320901839C160C5D" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_FB1D717D8D05994FC04A01839C16220E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_D136D578E7520731201F01839C1680C3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_FB1D717D8D05994FC04A01839C16220E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_D136D578E7520731201F01839C1680C3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_355DEB695666EA1DAFBA01839C160C32" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_FB1D717D8D05994FC04A01839C16220E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_355DEB695666EA1DAFBA01839C160C32" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_65EE9BF643913636E28D01839C168C73" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_FB1D717D8D05994FC04A01839C16220E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_65EE9BF643913636E28D01839C168C73" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_D2D00737FC766273C8EB01839C1616AB" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_FB1D717D8D05994FC04A01839C16220E" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_D2D00737FC766273C8EB01839C1616AB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_56369ECEEBA5C21A078201839C16E4DA" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_BBCC4D405B279D6E320901839C160C5D" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_56369ECEEBA5C21A078201839C16E4DA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_F3159B7003EB0C89CEFF01839C16E865" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_56369ECEEBA5C21A078201839C16E4DA" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_F3159B7003EB0C89CEFF01839C16E865" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_EmployeeServiceShareBasedCompensationNonvestedAwardsIssuedInPeriodTotalCompensationCostNotYetRecognized" xlink:label="loc_ob_EmployeeServiceShareBasedCompensationNonvestedAwardsIssuedInPeriodTotalCompensationCostNotYetRecognized_07DC5A6EAD4CBE56394001839C165EAA" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_56369ECEEBA5C21A078201839C16E4DA" xlink:to="loc_ob_EmployeeServiceShareBasedCompensationNonvestedAwardsIssuedInPeriodTotalCompensationCostNotYetRecognized_07DC5A6EAD4CBE56394001839C165EAA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_F767C7F3CB7F2975C15A01839C167F53" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_56369ECEEBA5C21A078201839C16E4DA" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_F767C7F3CB7F2975C15A01839C167F53" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/EmployeeShareBasedIncentiveCompensationPlansTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/FairValueOfFinancialInstruments" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/FairValueOfFinancialInstrumentsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_BC78066EBA4BA2D3F12369FD0DA266C3" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTable" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_D7B67E31163616CDADDA69FD0DA1BE61" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_BC78066EBA4BA2D3F12369FD0DA266C3" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_D7B67E31163616CDADDA69FD0DA1BE61" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_21AD82682005E62E9DE969FD0DA15BFC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_D7B67E31163616CDADDA69FD0DA1BE61" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_21AD82682005E62E9DE969FD0DA15BFC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_1FE4EFD8B60F7DD097A06AA97C507869_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_21AD82682005E62E9DE969FD0DA15BFC" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_1FE4EFD8B60F7DD097A06AA97C507869_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_1F58589B4BD26B62F40969FD0DA1223E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_21AD82682005E62E9DE969FD0DA15BFC" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_1F58589B4BD26B62F40969FD0DA1223E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_1FE4EFD8B60F7DD097A06AA97C507869" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_1F58589B4BD26B62F40969FD0DA1223E" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_1FE4EFD8B60F7DD097A06AA97C507869" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_EF93283788B14567735869FD0DA15F8A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_1F58589B4BD26B62F40969FD0DA1223E" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_EF93283788B14567735869FD0DA15F8A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_E1823EBE76450DF41F3569FD0DA17B53" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_1F58589B4BD26B62F40969FD0DA1223E" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_E1823EBE76450DF41F3569FD0DA17B53" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_8B875E43A3FFE09655D969FD0DA29E82" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_D7B67E31163616CDADDA69FD0DA1BE61" xlink:to="loc_dei_LegalEntityAxis_8B875E43A3FFE09655D969FD0DA29E82" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E0B179B2C8EDD6458E7969FD0DA2823F_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_8B875E43A3FFE09655D969FD0DA29E82" xlink:to="loc_dei_EntityDomain_E0B179B2C8EDD6458E7969FD0DA2823F_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_E0B179B2C8EDD6458E7969FD0DA2823F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_8B875E43A3FFE09655D969FD0DA29E82" xlink:to="loc_dei_EntityDomain_E0B179B2C8EDD6458E7969FD0DA2823F" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_OnebeaconUSHoldingsIncMember" xlink:label="loc_ob_OnebeaconUSHoldingsIncMember_E57821E1B7FFC998D27969FD0DA25221" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_E0B179B2C8EDD6458E7969FD0DA2823F" xlink:to="loc_ob_OnebeaconUSHoldingsIncMember_E57821E1B7FFC998D27969FD0DA25221" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtAndCapitalLeaseObligations" xlink:label="loc_us-gaap_DebtAndCapitalLeaseObligations_9FC8557D75910C8C61B969FD0DA22077" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_BC78066EBA4BA2D3F12369FD0DA266C3" xlink:to="loc_us-gaap_DebtAndCapitalLeaseObligations_9FC8557D75910C8C61B969FD0DA22077" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/IncomeTaxes" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/IncomeTaxesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxContingencyLineItems" xlink:label="loc_us-gaap_IncomeTaxContingencyLineItems_9E7F8C27D1328F5415806A860925A6D5" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxContingencyTable" xlink:label="loc_us-gaap_IncomeTaxContingencyTable_2A20093CF6E4AE6A408F6A860924BEBF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_9E7F8C27D1328F5415806A860925A6D5" xlink:to="loc_us-gaap_IncomeTaxContingencyTable_2A20093CF6E4AE6A408F6A860924BEBF" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="ob-20140630.xsd#ob_TaxAssessmentYearAxis" xlink:label="loc_ob_TaxAssessmentYearAxis_6C937DDB65676C06E0C56A8609248050" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxContingencyTable_2A20093CF6E4AE6A408F6A860924BEBF" xlink:to="loc_ob_TaxAssessmentYearAxis_6C937DDB65676C06E0C56A8609248050" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TaxAssessmentYearDomain" xlink:label="loc_ob_TaxAssessmentYearDomain_B3A27F8D668B0FE3815F6A860924DEAA_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ob_TaxAssessmentYearAxis_6C937DDB65676C06E0C56A8609248050" xlink:to="loc_ob_TaxAssessmentYearDomain_B3A27F8D668B0FE3815F6A860924DEAA_default" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TaxAssessmentYearDomain" xlink:label="loc_ob_TaxAssessmentYearDomain_B3A27F8D668B0FE3815F6A860924DEAA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ob_TaxAssessmentYearAxis_6C937DDB65676C06E0C56A8609248050" xlink:to="loc_ob_TaxAssessmentYearDomain_B3A27F8D668B0FE3815F6A860924DEAA" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TaxYear2005to2006Member" xlink:label="loc_ob_TaxYear2005to2006Member_1B050E27544153CBD0EE6A8609243E61" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_TaxAssessmentYearDomain_B3A27F8D668B0FE3815F6A860924DEAA" xlink:to="loc_ob_TaxYear2005to2006Member_1B050E27544153CBD0EE6A8609243E61" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TaxAssessmentYear2007To2009Member" xlink:label="loc_ob_TaxAssessmentYear2007To2009Member_23FF095A15E0AEEC0D676A860925A1DD" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_TaxAssessmentYearDomain_B3A27F8D668B0FE3815F6A860924DEAA" xlink:to="loc_ob_TaxAssessmentYear2007To2009Member_23FF095A15E0AEEC0D676A860925A1DD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_12A6FF794629F7DA67036A8609252820" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxContingencyTable_2A20093CF6E4AE6A408F6A860924BEBF" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_12A6FF794629F7DA67036A8609252820" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_570266743726737C37F06A8609253C97_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_12A6FF794629F7DA67036A8609252820" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_570266743726737C37F06A8609253C97_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_570266743726737C37F06A8609253C97" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_12A6FF794629F7DA67036A8609252820" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_570266743726737C37F06A8609253C97" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ForeignCountryMember" xlink:label="loc_us-gaap_ForeignCountryMember_FADA71BC03E9AA2561306A860925ED2A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_570266743726737C37F06A8609253C97" xlink:to="loc_us-gaap_ForeignCountryMember_FADA71BC03E9AA2561306A860925ED2A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InternalRevenueServiceIRSMember" xlink:label="loc_us-gaap_InternalRevenueServiceIRSMember_AD39EC8A607356BCFD716A86092558B6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_570266743726737C37F06A8609253C97" xlink:to="loc_us-gaap_InternalRevenueServiceIRSMember_AD39EC8A607356BCFD716A86092558B6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_D1B96D4E7E4CD9B8333F6A8609254BF1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_9E7F8C27D1328F5415806A860925A6D5" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_D1B96D4E7E4CD9B8333F6A8609254BF1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_5945517C23025F81E30D6A860925E6F6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_9E7F8C27D1328F5415806A860925A6D5" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_5945517C23025F81E30D6A860925E6F6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential_37757F6AEA2EAE7CE70E6A86092546E7" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_9E7F8C27D1328F5415806A860925A6D5" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential_37757F6AEA2EAE7CE70E6A86092546E7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExaminationIncreaseDecreaseInLiabilityFromPriorYear" xlink:label="loc_us-gaap_IncomeTaxExaminationIncreaseDecreaseInLiabilityFromPriorYear_1AF814FEA647F4F8227D6A860925405E" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_9E7F8C27D1328F5415806A860925A6D5" xlink:to="loc_us-gaap_IncomeTaxExaminationIncreaseDecreaseInLiabilityFromPriorYear_1AF814FEA647F4F8227D6A860925405E" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_IncomeTaxExaminationIncreaseDecreaseinLiabilityfromPriorYearRelatedtoItemswithUnallowableDeductions" xlink:label="loc_ob_IncomeTaxExaminationIncreaseDecreaseinLiabilityfromPriorYearRelatedtoItemswithUnallowableDeductions_1633F08434E10886A0626A86092591F0" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_9E7F8C27D1328F5415806A860925A6D5" xlink:to="loc_ob_IncomeTaxExaminationIncreaseDecreaseinLiabilityfromPriorYearRelatedtoItemswithUnallowableDeductions_1633F08434E10886A0626A86092591F0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_BC23D728AF1D6AE81FAA6A860926993A" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxContingencyLineItems_9E7F8C27D1328F5415806A860925A6D5" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_BC23D728AF1D6AE81FAA6A860926993A" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecurities" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesAssetBackedSecuritiesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_8CD3642A96F5EA010CEEFCADAA72A195" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_6556BEDFF91EF95B8819FCADAA632B7A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_8CD3642A96F5EA010CEEFCADAA72A195" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_6556BEDFF91EF95B8819FCADAA632B7A" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_E4E6C7B60D902D1DBC47FCADAA637425" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_6556BEDFF91EF95B8819FCADAA632B7A" xlink:to="loc_us-gaap_RangeAxis_E4E6C7B60D902D1DBC47FCADAA637425" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_450322F64D285508AA9FFCADAA63D2FC_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_E4E6C7B60D902D1DBC47FCADAA637425" xlink:to="loc_us-gaap_RangeMember_450322F64D285508AA9FFCADAA63D2FC_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_450322F64D285508AA9FFCADAA63D2FC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_E4E6C7B60D902D1DBC47FCADAA637425" xlink:to="loc_us-gaap_RangeMember_450322F64D285508AA9FFCADAA63D2FC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_60A1B0CCF387ABE5DB5FFCADAA63FE8D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_450322F64D285508AA9FFCADAA63D2FC" xlink:to="loc_us-gaap_MaximumMember_60A1B0CCF387ABE5DB5FFCADAA63FE8D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_2D1B3B8082358E93E255FCADAA633B66" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_6556BEDFF91EF95B8819FCADAA632B7A" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_2D1B3B8082358E93E255FCADAA633B66" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_2D1B3B8082358E93E255FCADAA633B66" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_2D1B3B8082358E93E255FCADAA633B66" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CommercialMortgageBackedSecuritiesFixedRateMember" xlink:label="loc_ob_CommercialMortgageBackedSecuritiesFixedRateMember_B9F3228C60916B756D73FCADAA6309C1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_ob_CommercialMortgageBackedSecuritiesFixedRateMember_B9F3228C60916B756D73FCADAA6309C1" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CommercialMortgageBackedSecuritiesFloatingRateMember" xlink:label="loc_ob_CommercialMortgageBackedSecuritiesFloatingRateMember_2FF9BBC8FED3B116FCE6FCADAA638A33" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_ob_CommercialMortgageBackedSecuritiesFloatingRateMember_2FF9BBC8FED3B116FCE6FCADAA638A33" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember" xlink:label="loc_us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember_91EBC413468DDCB82A69FCADAA63665C" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember_91EBC413468DDCB82A69FCADAA63665C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember" xlink:label="loc_us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember_1FECB5F5960841B81314FCADAA6373EF" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember_1FECB5F5960841B81314FCADAA6373EF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember" xlink:label="loc_us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember_EA01FCD633A8D67901B2FCADAA633E56" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember_EA01FCD633A8D67901B2FCADAA633E56" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember" xlink:label="loc_us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember_54529D29F9D6FE437820FCADAA634258" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember_54529D29F9D6FE437820FCADAA634258" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_037F8927C506882A018CFCADAA6348BD" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_037F8927C506882A018CFCADAA6348BD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommercialMortgageBackedSecuritiesMember" xlink:label="loc_us-gaap_CommercialMortgageBackedSecuritiesMember_DCA8DE9D56EA2C632E1FFCADAA63FEDD" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_CommercialMortgageBackedSecuritiesMember_DCA8DE9D56EA2C632E1FFCADAA63FEDD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember" xlink:label="loc_us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember_93182F05F22F0C8016F0FCADAA639A29" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember_93182F05F22F0C8016F0FCADAA639A29" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MortgageBackedSecuritiesMember" xlink:label="loc_us-gaap_MortgageBackedSecuritiesMember_B98725E34AE323F177C4FCADAA63DAF3" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_MortgageBackedSecuritiesMember_B98725E34AE323F177C4FCADAA63DAF3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CollateralizedCreditCardSecuritiesMember" xlink:label="loc_us-gaap_CollateralizedCreditCardSecuritiesMember_CB5D4EFFAF07B2A19DA7FCADAA639DD4" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_CollateralizedCreditCardSecuritiesMember_CB5D4EFFAF07B2A19DA7FCADAA639DD4" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CollateralizedAutoLoansMember" xlink:label="loc_us-gaap_CollateralizedAutoLoansMember_7DF0C830CB8C484CF34FFCADAA63E779" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_CollateralizedAutoLoansMember_7DF0C830CB8C484CF34FFCADAA63E779" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CollateralizedSecuritiesOtherMember" xlink:label="loc_us-gaap_CollateralizedSecuritiesOtherMember_514049C87479D68C05A6FCADAA63CD53" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_CollateralizedSecuritiesOtherMember_514049C87479D68C05A6FCADAA63CD53" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember" xlink:label="loc_us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember_A70C545EC5B41A39F7EFFCADAA63839E" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember_A70C545EC5B41A39F7EFFCADAA63839E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetBackedSecuritiesMember" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_C07D4CA46D746DF932B0FCADAA6383A7" xlink:type="locator" />
    <definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_C07D4CA46D746DF932B0FCADAA6383A7" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_NonPrimeResidentialMortgageBackedSecurityMember" xlink:label="loc_ob_NonPrimeResidentialMortgageBackedSecurityMember_88714C22FC6DA334BD06FCADAA72E830" xlink:type="locator" />
    <definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_5030BD8E73AA43BF12DCFCADAA63B24D" xlink:to="loc_ob_NonPrimeResidentialMortgageBackedSecurityMember_88714C22FC6DA334BD06FCADAA72E830" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8440956CAC72AA454494FCADAA729DA7" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_6556BEDFF91EF95B8819FCADAA632B7A" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8440956CAC72AA454494FCADAA729DA7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_77134E8C10D1C9C4134BFCADAA72AB9B_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8440956CAC72AA454494FCADAA729DA7" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_77134E8C10D1C9C4134BFCADAA72AB9B_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_77134E8C10D1C9C4134BFCADAA72AB9B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8440956CAC72AA454494FCADAA729DA7" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_77134E8C10D1C9C4134BFCADAA72AB9B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_99EF83889352D776FCF4FCADAA72FAAA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_77134E8C10D1C9C4134BFCADAA72AB9B" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_99EF83889352D776FCF4FCADAA72FAAA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_DBD698C08586CE254675FCADAA72E1AE" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_77134E8C10D1C9C4134BFCADAA72AB9B" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_DBD698C08586CE254675FCADAA72E1AE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_47FE97F1D5ABA049E0AFFCADAA72F840" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_77134E8C10D1C9C4134BFCADAA72AB9B" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_47FE97F1D5ABA049E0AFFCADAA72F840" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_AverageBasisPointsofSubordination" xlink:label="loc_ob_AverageBasisPointsofSubordination_C0688E5D1098D9031845FCADAA72D0E0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_8CD3642A96F5EA010CEEFCADAA72A195" xlink:to="loc_ob_AverageBasisPointsofSubordination_C0688E5D1098D9031845FCADAA72D0E0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans" xlink:label="loc_us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans_B96693BED64FF5AF8655FCADAA729D85" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_8CD3642A96F5EA010CEEFCADAA72A195" xlink:to="loc_us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans_B96693BED64FF5AF8655FCADAA729D85" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_153E1C104FD5348BF601FCADAA725C0D" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_8CD3642A96F5EA010CEEFCADAA72A195" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_153E1C104FD5348BF601FCADAA725C0D" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesChangeInNetUnrealizedGainsOrLossesForLevel3AssetsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_15FC0A9FE877C7459CF1FCADA9D6AC80" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_EE7EA8C0261E86963CB9FCADA9D61A7F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_15FC0A9FE877C7459CF1FCADA9D6AC80" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_EE7EA8C0261E86963CB9FCADA9D61A7F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_F9D0D3910848551B1AFBFCADA9D6F80A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_EE7EA8C0261E86963CB9FCADA9D61A7F" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_F9D0D3910848551B1AFBFCADA9D6F80A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8FC36DC16D10AB9EE195FCADA9D69612_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_F9D0D3910848551B1AFBFCADA9D6F80A" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8FC36DC16D10AB9EE195FCADA9D69612_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8FC36DC16D10AB9EE195FCADA9D69612" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_F9D0D3910848551B1AFBFCADA9D6F80A" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8FC36DC16D10AB9EE195FCADA9D69612" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_ABA99D1C312165CA5D8EFCADA9D6AF72" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8FC36DC16D10AB9EE195FCADA9D69612" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_ABA99D1C312165CA5D8EFCADA9D6AF72" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_55E927C92ED003764C08FCADA9D636BB" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_EE7EA8C0261E86963CB9FCADA9D61A7F" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_55E927C92ED003764C08FCADA9D636BB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_7530D5F781F57F80DF7BFCADA9D66F4F_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_55E927C92ED003764C08FCADA9D636BB" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_7530D5F781F57F80DF7BFCADA9D66F4F_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_7530D5F781F57F80DF7BFCADA9D66F4F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_55E927C92ED003764C08FCADA9D636BB" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_7530D5F781F57F80DF7BFCADA9D66F4F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FixedMaturitiesMember" xlink:label="loc_us-gaap_FixedMaturitiesMember_59D7504D71129B0F27A5FCADA9D643D5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_7530D5F781F57F80DF7BFCADA9D66F4F" xlink:to="loc_us-gaap_FixedMaturitiesMember_59D7504D71129B0F27A5FCADA9D643D5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShortTermInvestmentsMember" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_A10DCE757FBEC17EA6E2FCADA9D65D80" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_7530D5F781F57F80DF7BFCADA9D66F4F" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_A10DCE757FBEC17EA6E2FCADA9D65D80" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquitySecuritiesMember" xlink:label="loc_us-gaap_EquitySecuritiesMember_B3104E0BC805FACBBD5BFCADA9D649A1" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_7530D5F781F57F80DF7BFCADA9D66F4F" xlink:to="loc_us-gaap_EquitySecuritiesMember_B3104E0BC805FACBBD5BFCADA9D649A1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleDebtSecuritiesMember" xlink:label="loc_us-gaap_ConvertibleDebtSecuritiesMember_68DBF7A9B32FA7529024FCADA9D687D6" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_7530D5F781F57F80DF7BFCADA9D66F4F" xlink:to="loc_us-gaap_ConvertibleDebtSecuritiesMember_68DBF7A9B32FA7529024FCADA9D687D6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLongTermInvestmentsMember" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_A6643F316F7FC4291955FCADA9D634A3" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_7530D5F781F57F80DF7BFCADA9D66F4F" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_A6643F316F7FC4291955FCADA9D634A3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss" xlink:label="loc_us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss_FDBAFEA7344E1C17AB69FCADA9D6DE17" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_15FC0A9FE877C7459CF1FCADA9D6AC80" xlink:to="loc_us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss_FDBAFEA7344E1C17AB69FCADA9D6DE17" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesChangesInFairValueDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_F3010876AF61B9C22CFB6E925B9ACBA5" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_B53BC64821671EC0AD076E925B9A9F99" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_F3010876AF61B9C22CFB6E925B9ACBA5" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_B53BC64821671EC0AD076E925B9A9F99" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_840143CB4C771023FFFC6E925B9AB642" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_B53BC64821671EC0AD076E925B9A9F99" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_840143CB4C771023FFFC6E925B9AB642" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_30C447C5B265DC22BC206E925B9AC3E0_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_840143CB4C771023FFFC6E925B9AB642" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_30C447C5B265DC22BC206E925B9AC3E0_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_30C447C5B265DC22BC206E925B9AC3E0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_840143CB4C771023FFFC6E925B9AB642" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_30C447C5B265DC22BC206E925B9AC3E0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FixedMaturitiesMember" xlink:label="loc_us-gaap_FixedMaturitiesMember_0A399E4C3FCA19759C506E925B9AEBC3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_30C447C5B265DC22BC206E925B9AC3E0" xlink:to="loc_us-gaap_FixedMaturitiesMember_0A399E4C3FCA19759C506E925B9AEBC3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShortTermInvestmentsMember" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_916E0712DF04A215DEBC6E925B9A6211" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_30C447C5B265DC22BC206E925B9AC3E0" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_916E0712DF04A215DEBC6E925B9A6211" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_9296ED974E19FE45970F6E925B9AA226" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_30C447C5B265DC22BC206E925B9AC3E0" xlink:to="loc_us-gaap_CommonStockMember_9296ED974E19FE45970F6E925B9AA226" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleDebtSecuritiesMember" xlink:label="loc_us-gaap_ConvertibleDebtSecuritiesMember_763390326B8182A576F86E925B9A18C8" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_30C447C5B265DC22BC206E925B9AC3E0" xlink:to="loc_us-gaap_ConvertibleDebtSecuritiesMember_763390326B8182A576F86E925B9A18C8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLongTermInvestmentsMember" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_E4738B369D2C43B139AE6E925B9A9EA1" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_30C447C5B265DC22BC206E925B9AC3E0" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_E4738B369D2C43B139AE6E925B9A9EA1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesUnrealizedHoldingGainLossAbstract" xlink:label="loc_us-gaap_TradingSecuritiesUnrealizedHoldingGainLossAbstract_D327232044C63639E21B6E925B9A2FFC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_F3010876AF61B9C22CFB6E925B9ACBA5" xlink:to="loc_us-gaap_TradingSecuritiesUnrealizedHoldingGainLossAbstract_D327232044C63639E21B6E925B9A2FFC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss" xlink:label="loc_us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss_927A53CC7D04783EE09A6E925B9A86A5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TradingSecuritiesUnrealizedHoldingGainLossAbstract_D327232044C63639E21B6E925B9A2FFC" xlink:to="loc_us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss_927A53CC7D04783EE09A6E925B9A86A5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ForeignCurrencyTransactionGainLossUnrealized" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossUnrealized_2EFD3EDDAF709CA3DE756E925B9A8019" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TradingSecuritiesUnrealizedHoldingGainLossAbstract_D327232044C63639E21B6E925B9A2FFC" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossUnrealized_2EFD3EDDAF709CA3DE756E925B9A8019" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_NetUnrealizedGainLossAndForeignCurrencyGainLossOnTradingSecurities" xlink:label="loc_ob_NetUnrealizedGainLossAndForeignCurrencyGainLossOnTradingSecurities_C7D2C731C9C817EF8B4D6E925B9A443A" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TradingSecuritiesUnrealizedHoldingGainLossAbstract_D327232044C63639E21B6E925B9A2FFC" xlink:to="loc_ob_NetUnrealizedGainLossAndForeignCurrencyGainLossOnTradingSecurities_C7D2C731C9C817EF8B4D6E925B9A443A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ChangeInDeferredGainsLosses" xlink:label="loc_ob_ChangeInDeferredGainsLosses_AC6AAE0288CC13EAFC676E925B9AEE8F" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TradingSecuritiesUnrealizedHoldingGainLossAbstract_D327232044C63639E21B6E925B9A2FFC" xlink:to="loc_ob_ChangeInDeferredGainsLosses_AC6AAE0288CC13EAFC676E925B9AEE8F" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesConvertibleFixedMaturityInvestmentsAndOtherInvestmentsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9038CC44500046B117DD69FD0E686EDE" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_A39C6B43DF7DC599411A69FD0E674649" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9038CC44500046B117DD69FD0E686EDE" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_A39C6B43DF7DC599411A69FD0E674649" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_5832FBFEBA1BECC5332569FD0E671A95" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_A39C6B43DF7DC599411A69FD0E674649" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_5832FBFEBA1BECC5332569FD0E671A95" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_673980BED81A9593886269FD0E678824_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_5832FBFEBA1BECC5332569FD0E671A95" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_673980BED81A9593886269FD0E678824_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_673980BED81A9593886269FD0E678824" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_5832FBFEBA1BECC5332569FD0E671A95" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_673980BED81A9593886269FD0E678824" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RunoffMember" xlink:label="loc_ob_RunoffMember_52F47DC60612C773D7A669FD0E679B48" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_673980BED81A9593886269FD0E678824" xlink:to="loc_ob_RunoffMember_52F47DC60612C773D7A669FD0E679B48" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_C5CA1D60E880D0BF17F369FD0E67C824" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_A39C6B43DF7DC599411A69FD0E674649" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_C5CA1D60E880D0BF17F369FD0E67C824" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_4433927107DE2FB2D22569FD0E67923B_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_C5CA1D60E880D0BF17F369FD0E67C824" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_4433927107DE2FB2D22569FD0E67923B_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_4433927107DE2FB2D22569FD0E67923B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_C5CA1D60E880D0BF17F369FD0E67C824" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_4433927107DE2FB2D22569FD0E67923B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDiscontinuedOperationsMember" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_8654CCF499B053AFF3D169FD0E675CF6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_4433927107DE2FB2D22569FD0E67923B" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_8654CCF499B053AFF3D169FD0E675CF6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_80713916204FA5BDA26069FD0E676EB8" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_A39C6B43DF7DC599411A69FD0E674649" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_80713916204FA5BDA26069FD0E676EB8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_AA0C640D6D55FBCCD03869FD0E6717A9_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_80713916204FA5BDA26069FD0E676EB8" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_AA0C640D6D55FBCCD03869FD0E6717A9_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_AA0C640D6D55FBCCD03869FD0E6717A9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_80713916204FA5BDA26069FD0E676EB8" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_AA0C640D6D55FBCCD03869FD0E6717A9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_8052094B267EE42F856069FD0E676AC3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_AA0C640D6D55FBCCD03869FD0E6717A9" xlink:to="loc_us-gaap_CommonStockMember_8052094B267EE42F856069FD0E676AC3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleDebtSecuritiesMember" xlink:label="loc_us-gaap_ConvertibleDebtSecuritiesMember_96B08213A211FE32840469FD0E686C6A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_AA0C640D6D55FBCCD03869FD0E6717A9" xlink:to="loc_us-gaap_ConvertibleDebtSecuritiesMember_96B08213A211FE32840469FD0E686C6A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLongTermInvestmentsMember" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_46A48B890EFA9FD9545969FD0E6868AA" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_AA0C640D6D55FBCCD03869FD0E6717A9" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_46A48B890EFA9FD9545969FD0E6868AA" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CommonEquityConvertibleFixedAndOtherInvestmentsMember" xlink:label="loc_ob_CommonEquityConvertibleFixedAndOtherInvestmentsMember_A0B1EDE4F3C89FD9ED5B69FD0E685A17" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_AA0C640D6D55FBCCD03869FD0E6717A9" xlink:to="loc_ob_CommonEquityConvertibleFixedAndOtherInvestmentsMember_A0B1EDE4F3C89FD9ED5B69FD0E685A17" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_UnrestrictedCollateralFromCustomers" xlink:label="loc_ob_UnrestrictedCollateralFromCustomers_6EF7AAC55D9923770C7169FD0E68F581" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9038CC44500046B117DD69FD0E686EDE" xlink:to="loc_ob_UnrestrictedCollateralFromCustomers_6EF7AAC55D9923770C7169FD0E68F581" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesCost" xlink:label="loc_us-gaap_TradingSecuritiesCost_9032FAF17A9F6A05B5C669FD0E683F8A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9038CC44500046B117DD69FD0E686EDE" xlink:to="loc_us-gaap_TradingSecuritiesCost_9032FAF17A9F6A05B5C669FD0E683F8A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TradingSecuritiesGrossUnrealizedGain" xlink:label="loc_ob_TradingSecuritiesGrossUnrealizedGain_EFE5644ECBA5D446D80C69FD0E682351" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9038CC44500046B117DD69FD0E686EDE" xlink:to="loc_ob_TradingSecuritiesGrossUnrealizedGain_EFE5644ECBA5D446D80C69FD0E682351" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TradingSecuritiesGrossUnrealizedLoss" xlink:label="loc_ob_TradingSecuritiesGrossUnrealizedLoss_E26CBB54A3487CEC8D8E69FD0E681EF4" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9038CC44500046B117DD69FD0E686EDE" xlink:to="loc_ob_TradingSecuritiesGrossUnrealizedLoss_E26CBB54A3487CEC8D8E69FD0E681EF4" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TradingSecuritiesNetUnrealizedForeignCurrencyGainLoss" xlink:label="loc_ob_TradingSecuritiesNetUnrealizedForeignCurrencyGainLoss_267EF4E624E2EF0B9C0B69FD0E681F53" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9038CC44500046B117DD69FD0E686EDE" xlink:to="loc_ob_TradingSecuritiesNetUnrealizedForeignCurrencyGainLoss_267EF4E624E2EF0B9C0B69FD0E681F53" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesDebt" xlink:label="loc_us-gaap_TradingSecuritiesDebt_4A590205D1665FB2BB0869FD0E68498B" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9038CC44500046B117DD69FD0E686EDE" xlink:to="loc_us-gaap_TradingSecuritiesDebt_4A590205D1665FB2BB0869FD0E68498B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Investments" xlink:label="loc_us-gaap_Investments_0D4FB0550C265986B7C269FD0E6838FC" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9038CC44500046B117DD69FD0E686EDE" xlink:to="loc_us-gaap_Investments_0D4FB0550C265986B7C269FD0E6838FC" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesCorporateDebtSecuritesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_D1E16647CD2DE03E67FFFCADA979FC26" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_8F5CAB5F6FAC3ECBD306FCADA9790175" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_D1E16647CD2DE03E67FFFCADA979FC26" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_8F5CAB5F6FAC3ECBD306FCADA9790175" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CreditRatingStandardPoorsAxis" xlink:label="loc_us-gaap_CreditRatingStandardPoorsAxis_7093ECD0808C1F528B8BFCADA9798BF6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_8F5CAB5F6FAC3ECBD306FCADA9790175" xlink:to="loc_us-gaap_CreditRatingStandardPoorsAxis_7093ECD0808C1F528B8BFCADA9798BF6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ExternalCreditRatingStandardPoorsMember" xlink:label="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_0B5384403D3F303F1708FCADA97908F6_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditRatingStandardPoorsAxis_7093ECD0808C1F528B8BFCADA9798BF6" xlink:to="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_0B5384403D3F303F1708FCADA97908F6_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ExternalCreditRatingStandardPoorsMember" xlink:label="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_0B5384403D3F303F1708FCADA97908F6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditRatingStandardPoorsAxis_7093ECD0808C1F528B8BFCADA9798BF6" xlink:to="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_0B5384403D3F303F1708FCADA97908F6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StandardPoorsAARatingMember" xlink:label="loc_us-gaap_StandardPoorsAARatingMember_BA566B62B0169B8D8CFDFCADA9796844" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_0B5384403D3F303F1708FCADA97908F6" xlink:to="loc_us-gaap_StandardPoorsAARatingMember_BA566B62B0169B8D8CFDFCADA9796844" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StandardPoorsARatingMember" xlink:label="loc_us-gaap_StandardPoorsARatingMember_879F3727E86AC9594A5BFCADA9798786" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_0B5384403D3F303F1708FCADA97908F6" xlink:to="loc_us-gaap_StandardPoorsARatingMember_879F3727E86AC9594A5BFCADA9798786" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StandardPoorsBBBRatingMember" xlink:label="loc_us-gaap_StandardPoorsBBBRatingMember_7250201AEB1DA769BADEFCADA979778F" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_0B5384403D3F303F1708FCADA97908F6" xlink:to="loc_us-gaap_StandardPoorsBBBRatingMember_7250201AEB1DA769BADEFCADA979778F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StandardPoorsBBRatingMember" xlink:label="loc_us-gaap_StandardPoorsBBRatingMember_9CDD36D54739501A7B20FCADA979B871" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_0B5384403D3F303F1708FCADA97908F6" xlink:to="loc_us-gaap_StandardPoorsBBRatingMember_9CDD36D54739501A7B20FCADA979B871" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_OtherStandardPoorsRatingMember" xlink:label="loc_ob_OtherStandardPoorsRatingMember_2CCED15A15BE34244DFEFCADA9792A19" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_0B5384403D3F303F1708FCADA97908F6" xlink:to="loc_ob_OtherStandardPoorsRatingMember_2CCED15A15BE34244DFEFCADA9792A19" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_A15BD930FEF57F0C7601FCADA979971B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_8F5CAB5F6FAC3ECBD306FCADA9790175" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_A15BD930FEF57F0C7601FCADA979971B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_74C6CCB1D5C849BCB5B8FCADA979E2FF_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_A15BD930FEF57F0C7601FCADA979971B" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_74C6CCB1D5C849BCB5B8FCADA979E2FF_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_74C6CCB1D5C849BCB5B8FCADA979E2FF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_A15BD930FEF57F0C7601FCADA979971B" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_74C6CCB1D5C849BCB5B8FCADA979E2FF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_FEB002A455698877B4A3FCADA97989C5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_74C6CCB1D5C849BCB5B8FCADA979E2FF" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_FEB002A455698877B4A3FCADA97989C5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_6C2DD8C8528C624C01FEFCADA9792FAC" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_D1E16647CD2DE03E67FFFCADA979FC26" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_6C2DD8C8528C624C01FEFCADA9792FAC" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesFairValueMeasurementsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_02CE7F7FDAAA008194BA6F35626A12C0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_02CE7F7FDAAA008194BA6F35626A12C0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_AF0922EC104B6BFA92516F35626A8105" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_02CE7F7FDAAA008194BA6F35626A12C0" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_AF0922EC104B6BFA92516F35626A8105" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_AEEE3F058E911678DC176F35626A64CD_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_AF0922EC104B6BFA92516F35626A8105" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_AEEE3F058E911678DC176F35626A64CD_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_AEEE3F058E911678DC176F35626A64CD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_AF0922EC104B6BFA92516F35626A8105" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_AEEE3F058E911678DC176F35626A64CD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDiscontinuedOperationsMember" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_E5679834F8EE1E1F7C716F35626ABAC7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_AEEE3F058E911678DC176F35626A64CD" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_E5679834F8EE1E1F7C716F35626ABAC7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6F1CE17371CBC28536BA6F35626A20E9" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_02CE7F7FDAAA008194BA6F35626A12C0" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6F1CE17371CBC28536BA6F35626A20E9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_78E338B1DEAED89FD2366F35626A20BE_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6F1CE17371CBC28536BA6F35626A20E9" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_78E338B1DEAED89FD2366F35626A20BE_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_78E338B1DEAED89FD2366F35626A20BE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_6F1CE17371CBC28536BA6F35626A20E9" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_78E338B1DEAED89FD2366F35626A20BE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_0FA596235B522233F4DD6F35626A9519" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_78E338B1DEAED89FD2366F35626A20BE" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_0FA596235B522233F4DD6F35626A9519" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_74C026555CE6EDC960B06F35626B4EFC" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_02CE7F7FDAAA008194BA6F35626A12C0" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_74C026555CE6EDC960B06F35626B4EFC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_74C026555CE6EDC960B06F35626B4EFC" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_74C026555CE6EDC960B06F35626B4EFC" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_HedgeFundsMember" xlink:label="loc_us-gaap_HedgeFundsMember_5EAB64E2642DAA29D0926F35626BBB73" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_HedgeFundsMember_5EAB64E2642DAA29D0926F35626BBB73" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PrivateEquityFundsMember" xlink:label="loc_us-gaap_PrivateEquityFundsMember_8E88EA6941E0BF11C9516F35626B6F91" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_PrivateEquityFundsMember_8E88EA6941E0BF11C9516F35626B6F91" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CommunityReinvestmentVehicleMember" xlink:label="loc_ob_CommunityReinvestmentVehicleMember_9E00A4A05D4BBA1E05506F35626BB991" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_ob_CommunityReinvestmentVehicleMember_9E00A4A05D4BBA1E05506F35626BB991" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TrustCertificatesIssuedUponDissolutionofaPrivateEquityFundMember" xlink:label="loc_ob_TrustCertificatesIssuedUponDissolutionofaPrivateEquityFundMember_1942360C562F3183149D6F35626B0274" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_ob_TrustCertificatesIssuedUponDissolutionofaPrivateEquityFundMember_1942360C562F3183149D6F35626B0274" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SingleFundMember" xlink:label="loc_ob_SingleFundMember_0CD832BD0FC91E9614146F35626BA345" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_ob_SingleFundMember_0CD832BD0FC91E9614146F35626BA345" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TaxDevelopmentFundMember" xlink:label="loc_ob_TaxDevelopmentFundMember_FEC0D9365197902B29736F35626B9EE7" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_ob_TaxDevelopmentFundMember_FEC0D9365197902B29736F35626B9EE7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_37F6604B10BF68D9A1F36F35626B85E2" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_37F6604B10BF68D9A1F36F35626B85E2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_73B54A86EBDACCEF52306F35626B5169" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_73B54A86EBDACCEF52306F35626B5169" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MunicipalBondsMember" xlink:label="loc_us-gaap_MunicipalBondsMember_54363A99CA92CB0937966F35626BAFDB" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_MunicipalBondsMember_54363A99CA92CB0937966F35626BAFDB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetBackedSecuritiesMember" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_567F6A6C68C65C8187B96F35626B6428" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_567F6A6C68C65C8187B96F35626B6428" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommercialMortgageBackedSecuritiesMember" xlink:label="loc_us-gaap_CommercialMortgageBackedSecuritiesMember_35A4283C192A461ACA3D6F35626B68CB" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_CommercialMortgageBackedSecuritiesMember_35A4283C192A461ACA3D6F35626B68CB" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ForeignGovernmentExcludingUnitedStatesDebtSecuritiesMember" xlink:label="loc_ob_ForeignGovernmentExcludingUnitedStatesDebtSecuritiesMember_6B5E965D2770C220B3806F35626B1F5B" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_ob_ForeignGovernmentExcludingUnitedStatesDebtSecuritiesMember_6B5E965D2770C220B3806F35626B1F5B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PreferredStockMember" xlink:label="loc_us-gaap_PreferredStockMember_2ADEFDABFADD48EABC6C6F35626C7293" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_PreferredStockMember_2ADEFDABFADD48EABC6C6F35626C7293" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FixedMaturitiesMember" xlink:label="loc_us-gaap_FixedMaturitiesMember_C6BF9F392859592DF5F66F35626CE32C" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_FixedMaturitiesMember_C6BF9F392859592DF5F66F35626CE32C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShortTermInvestmentsMember" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_4C87A6A5893282AA234B6F35626C3378" xlink:type="locator" />
    <definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_4C87A6A5893282AA234B6F35626C3378" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_26FD37C7160A1F813A126F35626C4443" xlink:type="locator" />
    <definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_CommonStockMember_26FD37C7160A1F813A126F35626C4443" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleDebtSecuritiesMember" xlink:label="loc_us-gaap_ConvertibleDebtSecuritiesMember_24E0D0A83CB6B7A8E24D6F35626C049E" xlink:type="locator" />
    <definitionArc order="17" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_ConvertibleDebtSecuritiesMember_24E0D0A83CB6B7A8E24D6F35626C049E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLongTermInvestmentsMember" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_33383EF495E8FA9BF8436F35626C0607" xlink:type="locator" />
    <definitionArc order="18" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_F84E03E722D36480FDFB6F35626B86DF" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_33383EF495E8FA9BF8436F35626C0607" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_InvestmentSectorAxis" xlink:label="loc_invest_InvestmentSectorAxis_D1159643D0A50BE3A48E6F35626C8F35" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_02CE7F7FDAAA008194BA6F35626A12C0" xlink:to="loc_invest_InvestmentSectorAxis_D1159643D0A50BE3A48E6F35626C8F35" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_InvestmentSectorDomain" xlink:label="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_invest_InvestmentSectorAxis_D1159643D0A50BE3A48E6F35626C8F35" xlink:to="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_InvestmentSectorDomain" xlink:label="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_invest_InvestmentSectorAxis_D1159643D0A50BE3A48E6F35626C8F35" xlink:to="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ConsumerMember" xlink:label="loc_ob_ConsumerMember_54F7C322A08870CADEA96F35626C2CE6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94" xlink:to="loc_ob_ConsumerMember_54F7C322A08870CADEA96F35626C2CE6" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_IndustrialMember" xlink:label="loc_ob_IndustrialMember_8E1960D31D59EE711F8F6F35626CA765" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94" xlink:to="loc_ob_IndustrialMember_8E1960D31D59EE711F8F6F35626CA765" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FinancialsMember" xlink:label="loc_ob_FinancialsMember_CCA75B68E498E8A26C456F35626CB321" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94" xlink:to="loc_ob_FinancialsMember_CCA75B68E498E8A26C456F35626CB321" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CommunicationsMember" xlink:label="loc_ob_CommunicationsMember_8818D4B0B64113D606026F35626CA993" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94" xlink:to="loc_ob_CommunicationsMember_8818D4B0B64113D606026F35626CA993" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_EnergyMember" xlink:label="loc_ob_EnergyMember_0AE13E56EBE434568B4F6F35626CED28" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94" xlink:to="loc_ob_EnergyMember_0AE13E56EBE434568B4F6F35626CED28" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_BasicMaterialsMember" xlink:label="loc_ob_BasicMaterialsMember_F05795C5DE5D0AC4EE666F35626C4604" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94" xlink:to="loc_ob_BasicMaterialsMember_F05795C5DE5D0AC4EE666F35626C4604" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_UtilitiesMember" xlink:label="loc_ob_UtilitiesMember_B12B6DB8C5AE7EF6630A6F35626C251B" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94" xlink:to="loc_ob_UtilitiesMember_B12B6DB8C5AE7EF6630A6F35626C251B" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TechnologyMember" xlink:label="loc_ob_TechnologyMember_73D3D6ABA48BE24B94D06F35626D54B7" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94" xlink:to="loc_ob_TechnologyMember_73D3D6ABA48BE24B94D06F35626D54B7" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_OtherSectorMember" xlink:label="loc_ob_OtherSectorMember_51887B4D2DE42D6B06C36F35626D77E8" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_invest_InvestmentSectorDomain_DE92AFB2DAC74E6EC08B6F35626CDE94" xlink:to="loc_ob_OtherSectorMember_51887B4D2DE42D6B06C36F35626D77E8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3E6DAECE98CD27D5F8916F35626DA02C" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_02CE7F7FDAAA008194BA6F35626A12C0" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3E6DAECE98CD27D5F8916F35626DA02C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_B5280576D414F67A60676F35626D2DD6_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3E6DAECE98CD27D5F8916F35626DA02C" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_B5280576D414F67A60676F35626D2DD6_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_B5280576D414F67A60676F35626D2DD6" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3E6DAECE98CD27D5F8916F35626DA02C" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_B5280576D414F67A60676F35626D2DD6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_F63119E21803C84EDDA96F35626DE46A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_B5280576D414F67A60676F35626D2DD6" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_F63119E21803C84EDDA96F35626DE46A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_4719C34ABEC9F7FD1D686F35626D7B5C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_B5280576D414F67A60676F35626D2DD6" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_4719C34ABEC9F7FD1D686F35626D7B5C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_4FED8ADA5ED27BE03E826F35626D4CFF" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_B5280576D414F67A60676F35626D2DD6" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_4FED8ADA5ED27BE03E826F35626D4CFF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_8D0578C3268E130A2AB16F35626D7242" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_B5280576D414F67A60676F35626D2DD6" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_8D0578C3268E130A2AB16F35626D7242" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_MaximumPercentageDifferencesBetweenPricesProvidedbyPricingServicesConsideredOutliers" xlink:label="loc_ob_MaximumPercentageDifferencesBetweenPricesProvidedbyPricingServicesConsideredOutliers_59CC1CF7085A4ADC2F956F3C74FF1DE0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_ob_MaximumPercentageDifferencesBetweenPricesProvidedbyPricingServicesConsideredOutliers_59CC1CF7085A4ADC2F956F3C74FF1DE0" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ChangeInDeferredGainsLosses" xlink:label="loc_ob_ChangeInDeferredGainsLosses_1347D54C7E72FB7399686F35626D9EDF" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_ob_ChangeInDeferredGainsLosses_1347D54C7E72FB7399686F35626D9EDF" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Investments" xlink:label="loc_us-gaap_Investments_896798B5C18160367B636F35626D2120" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_us-gaap_Investments_896798B5C18160367B636F35626D2120" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_UnrestrictedCollateralFromCustomers" xlink:label="loc_ob_UnrestrictedCollateralFromCustomers_16E8D0B9533813EDB58E6F35626D578A" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_ob_UnrestrictedCollateralFromCustomers_16E8D0B9533813EDB58E6F35626D578A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_BA5318CAD456BBC7844A6F35626DCE85" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_BA5318CAD456BBC7844A6F35626DCE85" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_C7A9D62FAF2F72B2DC936F35626DB454" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_C7A9D62FAF2F72B2DC936F35626DB454" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InvestmentsPercentofTotal" xlink:label="loc_ob_InvestmentsPercentofTotal_7CFABA4B16D88FE1ABC36F35626D626D" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_ob_InvestmentsPercentofTotal_7CFABA4B16D88FE1ABC36F35626D626D" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PercentageOfFairValueInvestmentsUsingObservableInputs" xlink:label="loc_ob_PercentageOfFairValueInvestmentsUsingObservableInputs_0B7A05C3A7FA6328858D6F35626E0C30" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_ob_PercentageOfFairValueInvestmentsUsingObservableInputs_0B7A05C3A7FA6328858D6F35626E0C30" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherInvestments" xlink:label="loc_us-gaap_OtherInvestments_F6BBC909F349FEB54CD26F35626E041A" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_us-gaap_OtherInvestments_F6BBC909F349FEB54CD26F35626E041A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_NumberOfInvestments" xlink:label="loc_ob_NumberOfInvestments_B5F01E9FC6C3A859612A6F35626E8057" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_ob_NumberOfInvestments_B5F01E9FC6C3A859612A6F35626E8057" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FixedMaturitiesInvestmentsTradingSecuritiesDebtReclassifiedtoAssetsHeldforsale" xlink:label="loc_ob_FixedMaturitiesInvestmentsTradingSecuritiesDebtReclassifiedtoAssetsHeldforsale_110EFD2AAFD1EA70AC416F35626EBF97" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_ob_FixedMaturitiesInvestmentsTradingSecuritiesDebtReclassifiedtoAssetsHeldforsale_110EFD2AAFD1EA70AC416F35626EBF97" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PrivatePreferredStockPercentage" xlink:label="loc_ob_PrivatePreferredStockPercentage_D35B167CFDDEC13C90186F35626EFF8D" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_BA397DB4B93B030533836F35626D13DA" xlink:to="loc_ob_PrivatePreferredStockPercentage_D35B167CFDDEC13C90186F35626EFF8D" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesFairValueRollforwardDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_B6EB051DAE887E32695B69FD0E44B916" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_10EB585E7BE2F88C9F9369FD0E439C1A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_B6EB051DAE887E32695B69FD0E44B916" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_10EB585E7BE2F88C9F9369FD0E439C1A" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_5508AD7FC40580D5BFC669FD0E431621" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_10EB585E7BE2F88C9F9369FD0E439C1A" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_5508AD7FC40580D5BFC669FD0E431621" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8CCA7DE2A42FF027A1569FD0E43E957_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_5508AD7FC40580D5BFC669FD0E431621" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8CCA7DE2A42FF027A1569FD0E43E957_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8CCA7DE2A42FF027A1569FD0E43E957" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_5508AD7FC40580D5BFC669FD0E431621" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8CCA7DE2A42FF027A1569FD0E43E957" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TaxDevelopmentFundMember" xlink:label="loc_ob_TaxDevelopmentFundMember_A220AE7DCFB72A8EE0EC69FD0E435252" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8CCA7DE2A42FF027A1569FD0E43E957" xlink:to="loc_ob_TaxDevelopmentFundMember_A220AE7DCFB72A8EE0EC69FD0E435252" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FixedMaturitiesMember" xlink:label="loc_us-gaap_FixedMaturitiesMember_8110D3F6C47633195EEC69FD0E431BFD" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8CCA7DE2A42FF027A1569FD0E43E957" xlink:to="loc_us-gaap_FixedMaturitiesMember_8110D3F6C47633195EEC69FD0E431BFD" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquitySecuritiesMember" xlink:label="loc_us-gaap_EquitySecuritiesMember_0B0DFCC46AE47EE8F02869FD0E43AA2F" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8CCA7DE2A42FF027A1569FD0E43E957" xlink:to="loc_us-gaap_EquitySecuritiesMember_0B0DFCC46AE47EE8F02869FD0E43AA2F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleDebtSecuritiesMember" xlink:label="loc_us-gaap_ConvertibleDebtSecuritiesMember_30927D32EA94D39F150169FD0E432494" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8CCA7DE2A42FF027A1569FD0E43E957" xlink:to="loc_us-gaap_ConvertibleDebtSecuritiesMember_30927D32EA94D39F150169FD0E432494" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLongTermInvestmentsMember" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_43D8761CB594DE39E58C69FD0E448152" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8CCA7DE2A42FF027A1569FD0E43E957" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_43D8761CB594DE39E58C69FD0E448152" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_39A03290220D86797C2A69FD0E4449E6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_10EB585E7BE2F88C9F9369FD0E439C1A" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_39A03290220D86797C2A69FD0E4449E6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_005FE7A72E4FCB165E7E69FD0E44F047_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_39A03290220D86797C2A69FD0E4449E6" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_005FE7A72E4FCB165E7E69FD0E44F047_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_005FE7A72E4FCB165E7E69FD0E44F047" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_39A03290220D86797C2A69FD0E4449E6" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_005FE7A72E4FCB165E7E69FD0E44F047" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_462C4EF58546730B15CE6A45A9184BC0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_005FE7A72E4FCB165E7E69FD0E44F047" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_462C4EF58546730B15CE6A45A9184BC0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_D1A2EC515BB0185636336A20BF38867D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_005FE7A72E4FCB165E7E69FD0E44F047" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_D1A2EC515BB0185636336A20BF38867D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_939AA25690A2DA3E1F7569FD0E446C98" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_005FE7A72E4FCB165E7E69FD0E44F047" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_939AA25690A2DA3E1F7569FD0E446C98" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherInvestments" xlink:label="loc_us-gaap_OtherInvestments_22F2D8553F1108B8C68A69FD0E44123C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_B6EB051DAE887E32695B69FD0E44B916" xlink:to="loc_us-gaap_OtherInvestments_22F2D8553F1108B8C68A69FD0E44123C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_3315A24DC9DBA0D9882A69FD0E443A36" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_B6EB051DAE887E32695B69FD0E44B916" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_3315A24DC9DBA0D9882A69FD0E443A36" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_8B5D0CDCFE26A200E61469FD0E44A85B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_3315A24DC9DBA0D9882A69FD0E443A36" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_8B5D0CDCFE26A200E61469FD0E44A85B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments" xlink:label="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_E88B60730D9AC3DC387269FD0E4424D4" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_3315A24DC9DBA0D9882A69FD0E443A36" xlink:to="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_E88B60730D9AC3DC387269FD0E4424D4" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueAssetsMeasuredOnRecurringBasisGainLossIncludedInEarnings" xlink:label="loc_ob_FairValueAssetsMeasuredOnRecurringBasisGainLossIncludedInEarnings_7FF4A61E2EEB8266987669FD0E446F57" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_3315A24DC9DBA0D9882A69FD0E443A36" xlink:to="loc_ob_FairValueAssetsMeasuredOnRecurringBasisGainLossIncludedInEarnings_7FF4A61E2EEB8266987669FD0E446F57" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireInvestments" xlink:label="loc_us-gaap_PaymentsToAcquireInvestments_D9EC0424AB84FE7E332769FD0E44320E" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_3315A24DC9DBA0D9882A69FD0E443A36" xlink:to="loc_us-gaap_PaymentsToAcquireInvestments_D9EC0424AB84FE7E332769FD0E44320E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromSaleAndMaturityOfTradingSecuritiesHeldforinvestment" xlink:label="loc_us-gaap_ProceedsFromSaleAndMaturityOfTradingSecuritiesHeldforinvestment_ACB52FDFBED05E82957469FD0E45F840" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_3315A24DC9DBA0D9882A69FD0E443A36" xlink:to="loc_us-gaap_ProceedsFromSaleAndMaturityOfTradingSecuritiesHeldforinvestment_ACB52FDFBED05E82957469FD0E45F840" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueAssetsMeasuredOnRecurringBasisTransfersIn" xlink:label="loc_ob_FairValueAssetsMeasuredOnRecurringBasisTransfersIn_57791DB929001930B0A869FD0E45E5B9" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_3315A24DC9DBA0D9882A69FD0E443A36" xlink:to="loc_ob_FairValueAssetsMeasuredOnRecurringBasisTransfersIn_57791DB929001930B0A869FD0E45E5B9" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueAssetsMeasuredOnRecurringBasisTransfersOut" xlink:label="loc_ob_FairValueAssetsMeasuredOnRecurringBasisTransfersOut_A215534912B6F3F1C6F069FD0E4507BE" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_3315A24DC9DBA0D9882A69FD0E443A36" xlink:to="loc_ob_FairValueAssetsMeasuredOnRecurringBasisTransfersOut_A215534912B6F3F1C6F069FD0E4507BE" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueAssetsMeasuredonRecurringBasisTransfersoutRecategorized" xlink:label="loc_ob_FairValueAssetsMeasuredonRecurringBasisTransfersoutRecategorized_A5AD6A1090ADFC67A3DA69FD0E453345" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_B6EB051DAE887E32695B69FD0E44B916" xlink:to="loc_ob_FairValueAssetsMeasuredonRecurringBasisTransfersoutRecategorized_A5AD6A1090ADFC67A3DA69FD0E453345" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesFixedMaturityInvestmentGainsAndLossesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_34F94BEBF48A678B1E4169FD0E70AB00" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_AC3A3491B4754B89EFF169FD0E6ECAC3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_34F94BEBF48A678B1E4169FD0E70AB00" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_AC3A3491B4754B89EFF169FD0E6ECAC3" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_645D0E71B9E779F4B28769FD0E6EC52F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_AC3A3491B4754B89EFF169FD0E6ECAC3" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_645D0E71B9E779F4B28769FD0E6EC52F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_F33674A7887644EFE15D69FD0E6E9329_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_645D0E71B9E779F4B28769FD0E6EC52F" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_F33674A7887644EFE15D69FD0E6E9329_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_F33674A7887644EFE15D69FD0E6E9329" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_645D0E71B9E779F4B28769FD0E6EC52F" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_F33674A7887644EFE15D69FD0E6E9329" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDiscontinuedOperationsMember" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_65015FB7CBEC3123327F69FD0E6E7776" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_F33674A7887644EFE15D69FD0E6E9329" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_65015FB7CBEC3123327F69FD0E6E7776" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_970EFEFF9E1D2010302F69FD0E6F2815" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_AC3A3491B4754B89EFF169FD0E6ECAC3" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_970EFEFF9E1D2010302F69FD0E6F2815" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_5043D00454D257F9F11969FD0E6FF12A_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_970EFEFF9E1D2010302F69FD0E6F2815" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_5043D00454D257F9F11969FD0E6FF12A_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_5043D00454D257F9F11969FD0E6FF12A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_970EFEFF9E1D2010302F69FD0E6F2815" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_5043D00454D257F9F11969FD0E6FF12A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RunoffMember" xlink:label="loc_ob_RunoffMember_689459CA30FDAE7ED35969FD0E6FF61D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_5043D00454D257F9F11969FD0E6FF12A" xlink:to="loc_ob_RunoffMember_689459CA30FDAE7ED35969FD0E6FF61D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_DD01E5CE3D695833959669FD0E6FFCBC" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_AC3A3491B4754B89EFF169FD0E6ECAC3" xlink:to="loc_dei_LegalEntityAxis_DD01E5CE3D695833959669FD0E6FFCBC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_27A0CEBD33A599C9AFCE69FD0E6F22A0_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_DD01E5CE3D695833959669FD0E6FFCBC" xlink:to="loc_dei_EntityDomain_27A0CEBD33A599C9AFCE69FD0E6F22A0_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_27A0CEBD33A599C9AFCE69FD0E6F22A0" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_DD01E5CE3D695833959669FD0E6FFCBC" xlink:to="loc_dei_EntityDomain_27A0CEBD33A599C9AFCE69FD0E6F22A0" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RunoffMember" xlink:label="loc_ob_RunoffMember_0BAB8D6F01B73CE2BE3069FD0E6F18F3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_27A0CEBD33A599C9AFCE69FD0E6F22A0" xlink:to="loc_ob_RunoffMember_0BAB8D6F01B73CE2BE3069FD0E6F18F3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_D937114F69FE6D7FA31169FD0E6F2A63" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_AC3A3491B4754B89EFF169FD0E6ECAC3" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_D937114F69FE6D7FA31169FD0E6F2A63" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_A041AF953B0BE3AF856F69FD0E6F6FEB_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_D937114F69FE6D7FA31169FD0E6F2A63" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_A041AF953B0BE3AF856F69FD0E6F6FEB_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_A041AF953B0BE3AF856F69FD0E6F6FEB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_D937114F69FE6D7FA31169FD0E6F2A63" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_A041AF953B0BE3AF856F69FD0E6F6FEB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_92D3188B43A81D189A2369FD0E6FE770" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_A041AF953B0BE3AF856F69FD0E6F6FEB" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_92D3188B43A81D189A2369FD0E6FE770" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_F4A4E46590554AED867469FD0E6F84C2" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_A041AF953B0BE3AF856F69FD0E6F6FEB" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_F4A4E46590554AED867469FD0E6F84C2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MunicipalBondsMember" xlink:label="loc_us-gaap_MunicipalBondsMember_DA123F7DE4EC584529AC69FD0E6F345D" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_A041AF953B0BE3AF856F69FD0E6F6FEB" xlink:to="loc_us-gaap_MunicipalBondsMember_DA123F7DE4EC584529AC69FD0E6F345D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetBackedSecuritiesMember" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_262359EE24DC20A9697769FD0E7009C0" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_A041AF953B0BE3AF856F69FD0E6F6FEB" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_262359EE24DC20A9697769FD0E7009C0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember" xlink:label="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_AD6C1C95CE1CA6D7D50169FD0E70A563" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_A041AF953B0BE3AF856F69FD0E6F6FEB" xlink:to="loc_us-gaap_ForeignGovernmentDebtSecuritiesMember_AD6C1C95CE1CA6D7D50169FD0E70A563" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PreferredStockMember" xlink:label="loc_us-gaap_PreferredStockMember_73812E38B8C482E7B03069FD0E70FA96" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_A041AF953B0BE3AF856F69FD0E6F6FEB" xlink:to="loc_us-gaap_PreferredStockMember_73812E38B8C482E7B03069FD0E70FA96" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FixedMaturitiesMember" xlink:label="loc_us-gaap_FixedMaturitiesMember_FC76F5BCE6349F919F0169FD0E7036CA" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_A041AF953B0BE3AF856F69FD0E6F6FEB" xlink:to="loc_us-gaap_FixedMaturitiesMember_FC76F5BCE6349F919F0169FD0E7036CA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesCost" xlink:label="loc_us-gaap_TradingSecuritiesCost_EF275DA0B59E18E4801269FD0E70B961" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_34F94BEBF48A678B1E4169FD0E70AB00" xlink:to="loc_us-gaap_TradingSecuritiesCost_EF275DA0B59E18E4801269FD0E70B961" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TradingSecuritiesGrossUnrealizedGain" xlink:label="loc_ob_TradingSecuritiesGrossUnrealizedGain_B92FE68BA038FC8BB4A669FD0E707CDF" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_34F94BEBF48A678B1E4169FD0E70AB00" xlink:to="loc_ob_TradingSecuritiesGrossUnrealizedGain_B92FE68BA038FC8BB4A669FD0E707CDF" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TradingSecuritiesGrossUnrealizedLoss" xlink:label="loc_ob_TradingSecuritiesGrossUnrealizedLoss_5B4F10199B829FEC0B7469FD0E709F46" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_34F94BEBF48A678B1E4169FD0E70AB00" xlink:to="loc_ob_TradingSecuritiesGrossUnrealizedLoss_5B4F10199B829FEC0B7469FD0E709F46" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TradingSecuritiesNetUnrealizedForeignCurrencyGainLoss" xlink:label="loc_ob_TradingSecuritiesNetUnrealizedForeignCurrencyGainLoss_9F6E7A36B7BBC58636C369FD0E702BE2" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_34F94BEBF48A678B1E4169FD0E70AB00" xlink:to="loc_ob_TradingSecuritiesNetUnrealizedForeignCurrencyGainLoss_9F6E7A36B7BBC58636C369FD0E702BE2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesDebt" xlink:label="loc_us-gaap_TradingSecuritiesDebt_E1C083DB361D27A9789569FD0E7060C0" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_34F94BEBF48A678B1E4169FD0E70AB00" xlink:to="loc_us-gaap_TradingSecuritiesDebt_E1C083DB361D27A9789569FD0E7060C0" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesNetInvestmentIncomeDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_689896A7E1D9D3ED589269FD0E833392" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_F739DC90A178C108A6B069FD0E822C51" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_689896A7E1D9D3ED589269FD0E833392" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_F739DC90A178C108A6B069FD0E822C51" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_AA0E41FDB8FB62FCA39D69FD0E8200AA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_F739DC90A178C108A6B069FD0E822C51" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_AA0E41FDB8FB62FCA39D69FD0E8200AA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8AD95AAFA47724D07C169FD0E82373E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_AA0E41FDB8FB62FCA39D69FD0E8200AA" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8AD95AAFA47724D07C169FD0E82373E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8AD95AAFA47724D07C169FD0E82373E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_AA0E41FDB8FB62FCA39D69FD0E8200AA" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8AD95AAFA47724D07C169FD0E82373E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FixedMaturitiesMember" xlink:label="loc_us-gaap_FixedMaturitiesMember_5AD9C2B5D840656D2DA069FD0E821937" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8AD95AAFA47724D07C169FD0E82373E" xlink:to="loc_us-gaap_FixedMaturitiesMember_5AD9C2B5D840656D2DA069FD0E821937" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShortTermInvestmentsMember" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_571C0003A0F7EF2EF19F69FD0E827ACC" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8AD95AAFA47724D07C169FD0E82373E" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_571C0003A0F7EF2EF19F69FD0E827ACC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_DC323B3EBEF15490F83369FD0E82AC75" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8AD95AAFA47724D07C169FD0E82373E" xlink:to="loc_us-gaap_CommonStockMember_DC323B3EBEF15490F83369FD0E82AC75" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleDebtSecuritiesMember" xlink:label="loc_us-gaap_ConvertibleDebtSecuritiesMember_BAB2C6D2113094CC166869FD0E82339F" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8AD95AAFA47724D07C169FD0E82373E" xlink:to="loc_us-gaap_ConvertibleDebtSecuritiesMember_BAB2C6D2113094CC166869FD0E82339F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLongTermInvestmentsMember" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_F6C9C445EDC37E739AE469FD0E83EA1E" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_C8AD95AAFA47724D07C169FD0E82373E" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_F6C9C445EDC37E739AE469FD0E83EA1E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestAndDividendIncomeOperating" xlink:label="loc_us-gaap_InterestAndDividendIncomeOperating_119EB1A4764B5F1814AC69FD0E83A77E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_689896A7E1D9D3ED589269FD0E833392" xlink:to="loc_us-gaap_InterestAndDividendIncomeOperating_119EB1A4764B5F1814AC69FD0E83A77E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InvestmentIncomeInvestmentExpense" xlink:label="loc_us-gaap_InvestmentIncomeInvestmentExpense_7C442BC17C228DACCE2669FD0E83DFA0" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_689896A7E1D9D3ED589269FD0E833392" xlink:to="loc_us-gaap_InvestmentIncomeInvestmentExpense_7C442BC17C228DACCE2669FD0E83DFA0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetInvestmentIncome" xlink:label="loc_us-gaap_NetInvestmentIncome_0AD7A0DA0CC9EEF5F49969FD0E835ED5" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_689896A7E1D9D3ED589269FD0E833392" xlink:to="loc_us-gaap_NetInvestmentIncome_0AD7A0DA0CC9EEF5F49969FD0E835ED5" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesNetRealizedInvestmentGainsLossesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9ACD389022B8945CFDF9FCADA8ECD9D1" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_14E960C0925293DADA20FCADA8ECD616" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9ACD389022B8945CFDF9FCADA8ECD9D1" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_14E960C0925293DADA20FCADA8ECD616" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_BF2185F57D8117F70C6EFCADA8EC2B50" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_14E960C0925293DADA20FCADA8ECD616" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_BF2185F57D8117F70C6EFCADA8EC2B50" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_50D89777C11281401FF0FCADA8EC1195_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_BF2185F57D8117F70C6EFCADA8EC2B50" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_50D89777C11281401FF0FCADA8EC1195_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_50D89777C11281401FF0FCADA8EC1195" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_BF2185F57D8117F70C6EFCADA8EC2B50" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_50D89777C11281401FF0FCADA8EC1195" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FixedMaturitiesMember" xlink:label="loc_us-gaap_FixedMaturitiesMember_7A40F298D4E1FF50074BFCADA8ECBBA7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_50D89777C11281401FF0FCADA8EC1195" xlink:to="loc_us-gaap_FixedMaturitiesMember_7A40F298D4E1FF50074BFCADA8ECBBA7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShortTermInvestmentsMember" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_3BF7B336B9C69945E515FCADA8EC30D0" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_50D89777C11281401FF0FCADA8EC1195" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_3BF7B336B9C69945E515FCADA8EC30D0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockMember" xlink:label="loc_us-gaap_CommonStockMember_601A9B5165924A1F123DFCADA8EC0D6E" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_50D89777C11281401FF0FCADA8EC1195" xlink:to="loc_us-gaap_CommonStockMember_601A9B5165924A1F123DFCADA8EC0D6E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleDebtSecuritiesMember" xlink:label="loc_us-gaap_ConvertibleDebtSecuritiesMember_83B95D8C790ED0E76C02FCADA8EC0334" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_50D89777C11281401FF0FCADA8EC1195" xlink:to="loc_us-gaap_ConvertibleDebtSecuritiesMember_83B95D8C790ED0E76C02FCADA8EC0334" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherLongTermInvestmentsMember" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_6979C1A5B7871671106FFCADA8EC2B47" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_50D89777C11281401FF0FCADA8EC1195" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_6979C1A5B7871671106FFCADA8EC2B47" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ChangeInDeferredGainsLosses" xlink:label="loc_ob_ChangeInDeferredGainsLosses_7C525AF68148C5E8A06DFCADA8EC1544" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9ACD389022B8945CFDF9FCADA8ECD9D1" xlink:to="loc_ob_ChangeInDeferredGainsLosses_7C525AF68148C5E8A06DFCADA8EC1544" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesRealizedGainLoss" xlink:label="loc_us-gaap_TradingSecuritiesRealizedGainLoss_16AF68DD12CAFC49AA83FCADA8ECE58E" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9ACD389022B8945CFDF9FCADA8ECD9D1" xlink:to="loc_us-gaap_TradingSecuritiesRealizedGainLoss_16AF68DD12CAFC49AA83FCADA8ECE58E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PayablesToBrokerDealersAndClearingOrganizations" xlink:label="loc_us-gaap_PayablesToBrokerDealersAndClearingOrganizations_8542F7BFBB48A34F2D6FFCADA8ECD257" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9ACD389022B8945CFDF9FCADA8ECD9D1" xlink:to="loc_us-gaap_PayablesToBrokerDealersAndClearingOrganizations_8542F7BFBB48A34F2D6FFCADA8ECD257" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReceivablesFromBrokersDealersAndClearingOrganizations" xlink:label="loc_us-gaap_ReceivablesFromBrokersDealersAndClearingOrganizations_0EFD9AE7C84F1C8496F0FCADA8ECE6D3" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_9ACD389022B8945CFDF9FCADA8ECD9D1" xlink:to="loc_us-gaap_ReceivablesFromBrokersDealersAndClearingOrganizations_0EFD9AE7C84F1C8496F0FCADA8ECE6D3" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesNetUnrealizedInvestmentGainsAndLossesDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesNonAgencySecuritiesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_37823AB363222F2BA400FCADA9C7894C" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_2EC477191AB60D260A2FFCADA9C708AA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_37823AB363222F2BA400FCADA9C7894C" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_2EC477191AB60D260A2FFCADA9C708AA" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_36BA59AB1E3AC6E5969EFCADA9C78F80" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_2EC477191AB60D260A2FFCADA9C708AA" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_36BA59AB1E3AC6E5969EFCADA9C78F80" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_BA93A1C7A0B5EF9A344AFCADA9C7983B_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_36BA59AB1E3AC6E5969EFCADA9C78F80" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_BA93A1C7A0B5EF9A344AFCADA9C7983B_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_BA93A1C7A0B5EF9A344AFCADA9C7983B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis_36BA59AB1E3AC6E5969EFCADA9C78F80" xlink:to="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_BA93A1C7A0B5EF9A344AFCADA9C7983B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResidentialPrimeFinancingReceivableMember" xlink:label="loc_us-gaap_ResidentialPrimeFinancingReceivableMember_63251C538792E1FF5236FCADA9C71660" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_BA93A1C7A0B5EF9A344AFCADA9C7983B" xlink:to="loc_us-gaap_ResidentialPrimeFinancingReceivableMember_63251C538792E1FF5236FCADA9C71660" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResidentialSubprimeFinancingReceivableMember" xlink:label="loc_us-gaap_ResidentialSubprimeFinancingReceivableMember_C39A14F9F51214387E1FFCADA9C72862" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_BA93A1C7A0B5EF9A344AFCADA9C7983B" xlink:to="loc_us-gaap_ResidentialSubprimeFinancingReceivableMember_C39A14F9F51214387E1FFCADA9C72862" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecurityIssuanceYearAxis" xlink:label="loc_ob_SecurityIssuanceYearAxis_43919D9775BBAA348BFAFCADA9C71D2B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_2EC477191AB60D260A2FFCADA9C708AA" xlink:to="loc_ob_SecurityIssuanceYearAxis_43919D9775BBAA348BFAFCADA9C71D2B" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecurityIssuanceYearDomain" xlink:label="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ob_SecurityIssuanceYearAxis_43919D9775BBAA348BFAFCADA9C71D2B" xlink:to="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C_default" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecurityIssuanceYearDomain" xlink:label="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ob_SecurityIssuanceYearAxis_43919D9775BBAA348BFAFCADA9C71D2B" xlink:to="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecuritiesIssuedin2004Member" xlink:label="loc_ob_SecuritiesIssuedin2004Member_152C1BA3D926A1A1EB4BFCADA9C728FD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:to="loc_ob_SecuritiesIssuedin2004Member_152C1BA3D926A1A1EB4BFCADA9C728FD" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecuritiesIssuedIn2005Member" xlink:label="loc_ob_SecuritiesIssuedIn2005Member_B528DA2649868D6AE975FCADA9C788B2" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:to="loc_ob_SecuritiesIssuedIn2005Member_B528DA2649868D6AE975FCADA9C788B2" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecuritiesIssuedIn2006Member" xlink:label="loc_ob_SecuritiesIssuedIn2006Member_A5AA372984A4BFE01AA8FCADA9C74851" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:to="loc_ob_SecuritiesIssuedIn2006Member_A5AA372984A4BFE01AA8FCADA9C74851" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecuritiesIssuedIn2007Member" xlink:label="loc_ob_SecuritiesIssuedIn2007Member_0FF6F72A499D63467EABFCADA9C761C1" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:to="loc_ob_SecuritiesIssuedIn2007Member_0FF6F72A499D63467EABFCADA9C761C1" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecuritiesIssuedIn2008Member" xlink:label="loc_ob_SecuritiesIssuedIn2008Member_DCAF12536FDCC925E19EFCADA9C7FD3E" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:to="loc_ob_SecuritiesIssuedIn2008Member_DCAF12536FDCC925E19EFCADA9C7FD3E" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecuritiesIssuedin2009Member" xlink:label="loc_ob_SecuritiesIssuedin2009Member_C86CC9086DAB7139D877FCADA9C71431" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:to="loc_ob_SecuritiesIssuedin2009Member_C86CC9086DAB7139D877FCADA9C71431" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecuritiesIssuedIn2010Member" xlink:label="loc_ob_SecuritiesIssuedIn2010Member_C0356058A8B0B6EA063EFCADA9C78DAC" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:to="loc_ob_SecuritiesIssuedIn2010Member_C0356058A8B0B6EA063EFCADA9C78DAC" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecuritiesIssuedIn2011Member" xlink:label="loc_ob_SecuritiesIssuedIn2011Member_7A38D3F308017166722BFCADA9C7691A" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:to="loc_ob_SecuritiesIssuedIn2011Member_7A38D3F308017166722BFCADA9C7691A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecuritiesIssuedIn2012Member" xlink:label="loc_ob_SecuritiesIssuedIn2012Member_08029741548A5C3F3FF7FCADA9C7A8FE" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:to="loc_ob_SecuritiesIssuedIn2012Member_08029741548A5C3F3FF7FCADA9C7A8FE" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecuritiesIssuedIn2013Member" xlink:label="loc_ob_SecuritiesIssuedIn2013Member_71DA4375D0617E545B42FCADA9C7AA47" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:to="loc_ob_SecuritiesIssuedIn2013Member_71DA4375D0617E545B42FCADA9C7AA47" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SecuritiesIssuedin2014Member" xlink:label="loc_ob_SecuritiesIssuedin2014Member_2EA700801CF8CD5FC077FCADA9C74F86" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_SecurityIssuanceYearDomain_1E9900F9680B94CCE673FCADA9C70F2C" xlink:to="loc_ob_SecuritiesIssuedin2014Member_2EA700801CF8CD5FC077FCADA9C74F86" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0B388DD0414E17B71F63FCADA9C7ED0B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_2EC477191AB60D260A2FFCADA9C708AA" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0B388DD0414E17B71F63FCADA9C7ED0B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_493DEF0BB245CD5DFF2FFCADA9C70067_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0B388DD0414E17B71F63FCADA9C7ED0B" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_493DEF0BB245CD5DFF2FFCADA9C70067_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_493DEF0BB245CD5DFF2FFCADA9C70067" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0B388DD0414E17B71F63FCADA9C7ED0B" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_493DEF0BB245CD5DFF2FFCADA9C70067" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_568961813492FBA1F78DFCADA9C7E9F7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_493DEF0BB245CD5DFF2FFCADA9C70067" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_568961813492FBA1F78DFCADA9C7E9F7" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InvestmentByTrancheLevelsAxis" xlink:label="loc_ob_InvestmentByTrancheLevelsAxis_CCE1591924D131718F89FCADA9C77CC5" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_2EC477191AB60D260A2FFCADA9C708AA" xlink:to="loc_ob_InvestmentByTrancheLevelsAxis_CCE1591924D131718F89FCADA9C77CC5" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InvestmentTrancheLevelsDomain" xlink:label="loc_ob_InvestmentTrancheLevelsDomain_15ABDA39FA5F28094EEDFCADA9C72028_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ob_InvestmentByTrancheLevelsAxis_CCE1591924D131718F89FCADA9C77CC5" xlink:to="loc_ob_InvestmentTrancheLevelsDomain_15ABDA39FA5F28094EEDFCADA9C72028_default" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InvestmentTrancheLevelsDomain" xlink:label="loc_ob_InvestmentTrancheLevelsDomain_15ABDA39FA5F28094EEDFCADA9C72028" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ob_InvestmentByTrancheLevelsAxis_CCE1591924D131718F89FCADA9C77CC5" xlink:to="loc_ob_InvestmentTrancheLevelsDomain_15ABDA39FA5F28094EEDFCADA9C72028" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SuperSeniorMember" xlink:label="loc_ob_SuperSeniorMember_F614AE265D95A092B552FCADA9C777E5" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_InvestmentTrancheLevelsDomain_15ABDA39FA5F28094EEDFCADA9C72028" xlink:to="loc_ob_SuperSeniorMember_F614AE265D95A092B552FCADA9C777E5" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SeniorMember" xlink:label="loc_ob_SeniorMember_A999CE9885EC9ABC5EAAFCADA9C79ED0" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_InvestmentTrancheLevelsDomain_15ABDA39FA5F28094EEDFCADA9C72028" xlink:to="loc_ob_SeniorMember_A999CE9885EC9ABC5EAAFCADA9C79ED0" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SubordinateMember" xlink:label="loc_ob_SubordinateMember_74C4AE55186E6BCB1DD8FCADA9C76A17" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_InvestmentTrancheLevelsDomain_15ABDA39FA5F28094EEDFCADA9C72028" xlink:to="loc_ob_SubordinateMember_74C4AE55186E6BCB1DD8FCADA9C76A17" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_565440F4D823D6A7F521FCADA9C77592" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_2EC477191AB60D260A2FFCADA9C708AA" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_565440F4D823D6A7F521FCADA9C77592" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_BD369A05904640AC2B90FCADA9C73942_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_565440F4D823D6A7F521FCADA9C77592" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_BD369A05904640AC2B90FCADA9C73942_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_BD369A05904640AC2B90FCADA9C73942" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_565440F4D823D6A7F521FCADA9C77592" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_BD369A05904640AC2B90FCADA9C73942" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_64B96623A70D02A5FD81FCADA9C79D0F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_BD369A05904640AC2B90FCADA9C73942" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_64B96623A70D02A5FD81FCADA9C79D0F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommercialMortgageBackedSecuritiesMember" xlink:label="loc_us-gaap_CommercialMortgageBackedSecuritiesMember_76520CA78EF38A5FA44DFCADA9C7FBAF" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_BD369A05904640AC2B90FCADA9C73942" xlink:to="loc_us-gaap_CommercialMortgageBackedSecuritiesMember_76520CA78EF38A5FA44DFCADA9C7FBAF" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CommercialMortgageBackedSecuritiesFloatingRateMember" xlink:label="loc_ob_CommercialMortgageBackedSecuritiesFloatingRateMember_D7D220B8B143CC333D78FCADA9C7F71C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CommercialMortgageBackedSecuritiesMember_76520CA78EF38A5FA44DFCADA9C7FBAF" xlink:to="loc_ob_CommercialMortgageBackedSecuritiesFloatingRateMember_D7D220B8B143CC333D78FCADA9C7F71C" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CommercialMortgageBackedSecuritiesFixedRateMember" xlink:label="loc_ob_CommercialMortgageBackedSecuritiesFixedRateMember_995DC17170DD2D6E1FCFFCADA9C70BD8" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CommercialMortgageBackedSecuritiesMember_76520CA78EF38A5FA44DFCADA9C7FBAF" xlink:to="loc_ob_CommercialMortgageBackedSecuritiesFixedRateMember_995DC17170DD2D6E1FCFFCADA9C70BD8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember" xlink:label="loc_us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember_BCD14E15796BBBF3F154FCADA9C7E3A0" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_BD369A05904640AC2B90FCADA9C73942" xlink:to="loc_us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember_BCD14E15796BBBF3F154FCADA9C7E3A0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_162E970C33890227F0BBFCADA9C713A1" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_37823AB363222F2BA400FCADA9C7894C" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_162E970C33890227F0BBFCADA9C713A1" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesOtherInvestmentsDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_2142D43B518F71C47E0DFCADA9F53F87" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable" xlink:label="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_0637D6EB21F4B046CC3EFCADA9F54228" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_2142D43B518F71C47E0DFCADA9F53F87" xlink:to="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_0637D6EB21F4B046CC3EFCADA9F54228" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_8848C3DCB97AA7200189FCADA9F5934E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_0637D6EB21F4B046CC3EFCADA9F54228" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_8848C3DCB97AA7200189FCADA9F5934E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_8848C3DCB97AA7200189FCADA9F5934E" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_8848C3DCB97AA7200189FCADA9F5934E" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CommunityReinvestmentVehicleMember" xlink:label="loc_ob_CommunityReinvestmentVehicleMember_9630994CE7B7E7D32E39FCADA9F58A6A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_ob_CommunityReinvestmentVehicleMember_9630994CE7B7E7D32E39FCADA9F58A6A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_HedgeFundsCreditAndDistressedMember" xlink:label="loc_ob_HedgeFundsCreditAndDistressedMember_364A12A0B4E9D44FB8F2FCADA9F5B802" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_ob_HedgeFundsCreditAndDistressedMember_364A12A0B4E9D44FB8F2FCADA9F5B802" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_HedgeFundsBankLoanMember" xlink:label="loc_ob_HedgeFundsBankLoanMember_E7F7D5A4E50B8D00C97DFCADA9F5FB1D" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_ob_HedgeFundsBankLoanMember_E7F7D5A4E50B8D00C97DFCADA9F5FB1D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_HedgeFundsEquityMember" xlink:label="loc_us-gaap_HedgeFundsEquityMember_1CA36A6ED821E1F42CF8FCADA9F55CB1" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_us-gaap_HedgeFundsEquityMember_1CA36A6ED821E1F42CF8FCADA9F55CB1" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_HedgeFundsEquityActivistMember" xlink:label="loc_ob_HedgeFundsEquityActivistMember_5A5DA9CA3F34BDE76956FCADA9F56188" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_ob_HedgeFundsEquityActivistMember_5A5DA9CA3F34BDE76956FCADA9F56188" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_HedgeFundsMember" xlink:label="loc_us-gaap_HedgeFundsMember_7D9971B55510066F8BBDFCADA9F5FD99" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_us-gaap_HedgeFundsMember_7D9971B55510066F8BBDFCADA9F5FD99" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PrivateEquityInsuranceMember" xlink:label="loc_ob_PrivateEquityInsuranceMember_2FBFA3856FD9A1F6AF06FCADA9F533C6" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_ob_PrivateEquityInsuranceMember_2FBFA3856FD9A1F6AF06FCADA9F533C6" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PrivateEquityDistressedResidentialRealEstateMember" xlink:label="loc_ob_PrivateEquityDistressedResidentialRealEstateMember_F96E8BB11B6203F22ED5FCADA9F5D545" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_ob_PrivateEquityDistressedResidentialRealEstateMember_F96E8BB11B6203F22ED5FCADA9F5D545" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PrivateEquityEnergyInfrastructureAndServicesMember" xlink:label="loc_ob_PrivateEquityEnergyInfrastructureAndServicesMember_F7A477FE2BF63DF105D1FCADA9F5A964" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_ob_PrivateEquityEnergyInfrastructureAndServicesMember_F7A477FE2BF63DF105D1FCADA9F5A964" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PrivateEquityHealthcareMember" xlink:label="loc_ob_PrivateEquityHealthcareMember_ABB106F75D28E5F35BDAFCADA9F51FCE" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_ob_PrivateEquityHealthcareMember_ABB106F75D28E5F35BDAFCADA9F51FCE" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PrivateEquityMultiSectorMember" xlink:label="loc_ob_PrivateEquityMultiSectorMember_D289C85BCC2D31D6905FFCADA9F5C560" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_ob_PrivateEquityMultiSectorMember_D289C85BCC2D31D6905FFCADA9F5C560" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PrivateEquitySecondariesMember" xlink:label="loc_ob_PrivateEquitySecondariesMember_51ED4AE63D2A12C94310FCADA9F5CED1" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_ob_PrivateEquitySecondariesMember_51ED4AE63D2A12C94310FCADA9F5CED1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RealEstateFundsMember" xlink:label="loc_us-gaap_RealEstateFundsMember_7F008245FF3E450F61ECFCADA9F5E52B" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_us-gaap_RealEstateFundsMember_7F008245FF3E450F61ECFCADA9F5E52B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PrivateEquityFundsMember" xlink:label="loc_us-gaap_PrivateEquityFundsMember_3922164F1363E9AFDD09FCADA9F520BE" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_us-gaap_PrivateEquityFundsMember_3922164F1363E9AFDD09FCADA9F520BE" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_HedgeFundsAndPrivateEquityFundsMember" xlink:label="loc_ob_HedgeFundsAndPrivateEquityFundsMember_1ADFAFF7C0B51C3AB991FCADA9F51BB7" xlink:type="locator" />
    <definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_6151C86AAC465D39D1B6FCADA9F54FDF" xlink:to="loc_ob_HedgeFundsAndPrivateEquityFundsMember_1ADFAFF7C0B51C3AB991FCADA9F51BB7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_CF22A6131D24BDB5DDF3FCADA9F514E6" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_0637D6EB21F4B046CC3EFCADA9F54228" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_CF22A6131D24BDB5DDF3FCADA9F514E6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_C884B4C8A35145514F3EFCADA9F5ABE9_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_CF22A6131D24BDB5DDF3FCADA9F514E6" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_C884B4C8A35145514F3EFCADA9F5ABE9_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_C884B4C8A35145514F3EFCADA9F5ABE9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_CF22A6131D24BDB5DDF3FCADA9F514E6" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_C884B4C8A35145514F3EFCADA9F5ABE9" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyMonthlyMember" xlink:label="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyMonthlyMember_448B883B8BE373B407CCFCADA9F50605" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_C884B4C8A35145514F3EFCADA9F5ABE9" xlink:to="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyMonthlyMember_448B883B8BE373B407CCFCADA9F50605" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyQuarterlyMember" xlink:label="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyQuarterlyMember_7A0AF53BE54EAB039C11FCADA9F5D962" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_C884B4C8A35145514F3EFCADA9F5ABE9" xlink:to="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyQuarterlyMember_7A0AF53BE54EAB039C11FCADA9F5D962" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAnnualMember" xlink:label="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAnnualMember_688C0A7CA209A4AF526BFCADA9F5C94F" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_C884B4C8A35145514F3EFCADA9F5ABE9" xlink:to="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAnnualMember_688C0A7CA209A4AF526BFCADA9F5C94F" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis" xlink:label="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis_6B14F9776F6FDF2C3B08FCADA9F56E2E" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_0637D6EB21F4B046CC3EFCADA9F54228" xlink:to="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis_6B14F9776F6FDF2C3B08FCADA9F56E2E" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyDomain" xlink:label="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyDomain_BDEE5FE628D9A5363CA1FCADA9F59B37_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis_6B14F9776F6FDF2C3B08FCADA9F56E2E" xlink:to="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyDomain_BDEE5FE628D9A5363CA1FCADA9F59B37_default" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyDomain" xlink:label="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyDomain_BDEE5FE628D9A5363CA1FCADA9F59B37" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyAxis_6B14F9776F6FDF2C3B08FCADA9F56E2E" xlink:to="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyDomain_BDEE5FE628D9A5363CA1FCADA9F59B37" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InvestmentRedemptionNoticePeriod60To89DaysMember" xlink:label="loc_ob_InvestmentRedemptionNoticePeriod60To89DaysMember_F2E6B77D9247AF245118FCADA9F5FF21" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyDomain_BDEE5FE628D9A5363CA1FCADA9F59B37" xlink:to="loc_ob_InvestmentRedemptionNoticePeriod60To89DaysMember_F2E6B77D9247AF245118FCADA9F5FF21" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InvestmentRedemptionNoticePeriodOver120DaysMember" xlink:label="loc_ob_InvestmentRedemptionNoticePeriodOver120DaysMember_1E55F8A3F468C5985356FCADA9F5E79D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyDomain_BDEE5FE628D9A5363CA1FCADA9F59B37" xlink:to="loc_ob_InvestmentRedemptionNoticePeriodOver120DaysMember_1E55F8A3F468C5985356FCADA9F5E79D" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InvestmentRedemptionNoticePeriod90To119DaysMember" xlink:label="loc_ob_InvestmentRedemptionNoticePeriod90To119DaysMember_04961C65309327D71990FCADA9F5EE0A" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyDomain_BDEE5FE628D9A5363CA1FCADA9F59B37" xlink:to="loc_ob_InvestmentRedemptionNoticePeriod90To119DaysMember_04961C65309327D71990FCADA9F5EE0A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriodThirtyToFiftyNineDaysMember" xlink:label="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriodThirtyToFiftyNineDaysMember_0852019EF33C61E26C6AFCADA9F51B42" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionFrequencyDomain_BDEE5FE628D9A5363CA1FCADA9F59B37" xlink:to="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareInvestmentRedemptionNoticePeriodThirtyToFiftyNineDaysMember_0852019EF33C61E26C6AFCADA9F51B42" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodAxis" xlink:label="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodAxis_10762F3E4DD0954FA9EDFCADA9F513B8" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsTable_0637D6EB21F4B046CC3EFCADA9F54228" xlink:to="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodAxis_10762F3E4DD0954FA9EDFCADA9F513B8" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodDomain" xlink:label="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodDomain_4116E20AC90FECB5944EFCADA9F5CE24_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodAxis_10762F3E4DD0954FA9EDFCADA9F513B8" xlink:to="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodDomain_4116E20AC90FECB5944EFCADA9F5CE24_default" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodDomain" xlink:label="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodDomain_4116E20AC90FECB5944EFCADA9F5CE24" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodAxis_10762F3E4DD0954FA9EDFCADA9F513B8" xlink:to="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodDomain_4116E20AC90FECB5944EFCADA9F5CE24" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_LiquidatingInvestmentRemainingPeriod1To3YearsMember" xlink:label="loc_ob_LiquidatingInvestmentRemainingPeriod1To3YearsMember_447927E34777277988B4FCADA9F5000E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodDomain_4116E20AC90FECB5944EFCADA9F5CE24" xlink:to="loc_ob_LiquidatingInvestmentRemainingPeriod1To3YearsMember_447927E34777277988B4FCADA9F5000E" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_LiquidatingInvestmentRemainingPeriod3To5YearsMember" xlink:label="loc_ob_LiquidatingInvestmentRemainingPeriod3To5YearsMember_1FB27EE10DE0BCA382F4FCADA9F51A83" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodDomain_4116E20AC90FECB5944EFCADA9F5CE24" xlink:to="loc_ob_LiquidatingInvestmentRemainingPeriod3To5YearsMember_1FB27EE10DE0BCA382F4FCADA9F51A83" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_LiquidatingInvestmentRemainingPeriod5To10YearsMember" xlink:label="loc_ob_LiquidatingInvestmentRemainingPeriod5To10YearsMember_1441F1A9792D595B40E1FCADA9F5E438" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodDomain_4116E20AC90FECB5944EFCADA9F5CE24" xlink:to="loc_ob_LiquidatingInvestmentRemainingPeriod5To10YearsMember_1441F1A9792D595B40E1FCADA9F5E438" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_LiquidatingInvestmentRemainingPeriodOver10YearsMember" xlink:label="loc_ob_LiquidatingInvestmentRemainingPeriodOver10YearsMember_7A22C67F54F42FEE014FFCADA9F5B519" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLiquidatingInvestmentRemainingPeriodDomain_4116E20AC90FECB5944EFCADA9F5CE24" xlink:to="loc_ob_LiquidatingInvestmentRemainingPeriodOver10YearsMember_7A22C67F54F42FEE014FFCADA9F5B519" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherInvestments" xlink:label="loc_us-gaap_OtherInvestments_90D36120BB01BA3B6B17FCADA9F59B4F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_2142D43B518F71C47E0DFCADA9F53F87" xlink:to="loc_us-gaap_OtherInvestments_90D36120BB01BA3B6B17FCADA9F59B4F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TradingSecuritiesOther" xlink:label="loc_us-gaap_TradingSecuritiesOther_2644C99414B36BF276F0FCADA9F56AC9" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_2142D43B518F71C47E0DFCADA9F53F87" xlink:to="loc_us-gaap_TradingSecuritiesOther_2644C99414B36BF276F0FCADA9F56AC9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments" xlink:label="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments_492F7B70A4E87A61382AFCADA9F50788" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_2142D43B518F71C47E0DFCADA9F53F87" xlink:to="loc_us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareUnfundedCommittments_492F7B70A4E87A61382AFCADA9F50788" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_DistributionsFromInactiveHedgeFunds" xlink:label="loc_ob_DistributionsFromInactiveHedgeFunds_E32C543A31D73417303FFCADA9F517BF" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_2142D43B518F71C47E0DFCADA9F53F87" xlink:to="loc_ob_DistributionsFromInactiveHedgeFunds_E32C543A31D73417303FFCADA9F517BF" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareRedemptionRequest" xlink:label="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareRedemptionRequest_96E4551C4AC3F930E938FCADA9F59512" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems_2142D43B518F71C47E0DFCADA9F53F87" xlink:to="loc_ob_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareRedemptionRequest_96E4551C4AC3F930E938FCADA9F59512" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesSecuritiesClassifiedAsLevel3Details" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems" xlink:label="loc_us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems_68B22F20D9A7313BFC5569FD0E3B1D82" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsAssetsQuantitativeInformationTable" xlink:label="loc_us-gaap_FairValueInputsAssetsQuantitativeInformationTable_1BDB658C33147A9BE41969FD0E39F471" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems_68B22F20D9A7313BFC5569FD0E3B1D82" xlink:to="loc_us-gaap_FairValueInputsAssetsQuantitativeInformationTable_1BDB658C33147A9BE41969FD0E39F471" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CreditRatingStandardPoorsAxis" xlink:label="loc_us-gaap_CreditRatingStandardPoorsAxis_64EE6FF5AE95148BD10169FD0E393DF9" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInputsAssetsQuantitativeInformationTable_1BDB658C33147A9BE41969FD0E39F471" xlink:to="loc_us-gaap_CreditRatingStandardPoorsAxis_64EE6FF5AE95148BD10169FD0E393DF9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ExternalCreditRatingStandardPoorsMember" xlink:label="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_D8F9B853862CBC44039269FD0E3923BA_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditRatingStandardPoorsAxis_64EE6FF5AE95148BD10169FD0E393DF9" xlink:to="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_D8F9B853862CBC44039269FD0E3923BA_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ExternalCreditRatingStandardPoorsMember" xlink:label="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_D8F9B853862CBC44039269FD0E3923BA" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditRatingStandardPoorsAxis_64EE6FF5AE95148BD10169FD0E393DF9" xlink:to="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_D8F9B853862CBC44039269FD0E3923BA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StandardPoorsAAPlusRatingMember" xlink:label="loc_us-gaap_StandardPoorsAAPlusRatingMember_AFC0D0604C397795E63A69FD0E39FF23" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_D8F9B853862CBC44039269FD0E3923BA" xlink:to="loc_us-gaap_StandardPoorsAAPlusRatingMember_AFC0D0604C397795E63A69FD0E39FF23" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_StandardPoorsNRRatingMember" xlink:label="loc_ob_StandardPoorsNRRatingMember_F530DD67CF58AB6216A769FD0E3990BC" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_D8F9B853862CBC44039269FD0E3923BA" xlink:to="loc_ob_StandardPoorsNRRatingMember_F530DD67CF58AB6216A769FD0E3990BC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StandardPoorsAAARatingMember" xlink:label="loc_us-gaap_StandardPoorsAAARatingMember_21214E9F3ACC186057076A492304C4BC" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_D8F9B853862CBC44039269FD0E3923BA" xlink:to="loc_us-gaap_StandardPoorsAAARatingMember_21214E9F3ACC186057076A492304C4BC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByAssetClassAxis" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_5CE28EEFCD409ADE37E069FD0E3A70CC" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInputsAssetsQuantitativeInformationTable_1BDB658C33147A9BE41969FD0E39F471" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_5CE28EEFCD409ADE37E069FD0E3A70CC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_A86DC7837816535DBBCB69FD0E3A2D39_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_5CE28EEFCD409ADE37E069FD0E3A70CC" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_A86DC7837816535DBBCB69FD0E3A2D39_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_A86DC7837816535DBBCB69FD0E3A2D39" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_5CE28EEFCD409ADE37E069FD0E3A70CC" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_A86DC7837816535DBBCB69FD0E3A2D39" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommercialMortgageBackedSecuritiesMember" xlink:label="loc_us-gaap_CommercialMortgageBackedSecuritiesMember_89FA68FA33905A5BF0C869FD0E3A0D43" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_A86DC7837816535DBBCB69FD0E3A2D39" xlink:to="loc_us-gaap_CommercialMortgageBackedSecuritiesMember_89FA68FA33905A5BF0C869FD0E3A0D43" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResidentialMortgageBackedSecuritiesMember" xlink:label="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_44661ED3A367DDF11F7969FD0E3AA693" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_A86DC7837816535DBBCB69FD0E3A2D39" xlink:to="loc_us-gaap_ResidentialMortgageBackedSecuritiesMember_44661ED3A367DDF11F7969FD0E3AA693" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember" xlink:label="loc_us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember_73C2EE20311B6823C54169FD0E3A6DC6" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_A86DC7837816535DBBCB69FD0E3A2D39" xlink:to="loc_us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember_73C2EE20311B6823C54169FD0E3A6DC6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetBackedSecuritiesMember" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_CB127FB53CC487BDC8A469FD0E3AA625" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_A86DC7837816535DBBCB69FD0E3A2D39" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_CB127FB53CC487BDC8A469FD0E3AA625" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PreferredStockMember" xlink:label="loc_us-gaap_PreferredStockMember_9C195EC7DA6C6C07F4F069FD0E3A5604" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_A86DC7837816535DBBCB69FD0E3A2D39" xlink:to="loc_us-gaap_PreferredStockMember_9C195EC7DA6C6C07F4F069FD0E3A5604" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ValuationTechniqueAxis" xlink:label="loc_us-gaap_ValuationTechniqueAxis_718E75B22F4EA2C1846C69FD0E3A50B6" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueInputsAssetsQuantitativeInformationTable_1BDB658C33147A9BE41969FD0E39F471" xlink:to="loc_us-gaap_ValuationTechniqueAxis_718E75B22F4EA2C1846C69FD0E3A50B6" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="loc_us-gaap_ValuationTechniqueDomain_59D3790D3EC9D1A0D3F969FD0E3AE8E7_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_718E75B22F4EA2C1846C69FD0E3A50B6" xlink:to="loc_us-gaap_ValuationTechniqueDomain_59D3790D3EC9D1A0D3F969FD0E3AE8E7_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ValuationTechniqueDomain" xlink:label="loc_us-gaap_ValuationTechniqueDomain_59D3790D3EC9D1A0D3F969FD0E3AE8E7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_718E75B22F4EA2C1846C69FD0E3A50B6" xlink:to="loc_us-gaap_ValuationTechniqueDomain_59D3790D3EC9D1A0D3F969FD0E3AE8E7" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_DiscountedCashFlowValuationTechniqueMember" xlink:label="loc_ob_DiscountedCashFlowValuationTechniqueMember_A693221EA593AB516B3E69FD0E3A1483" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_59D3790D3EC9D1A0D3F969FD0E3AE8E7" xlink:to="loc_ob_DiscountedCashFlowValuationTechniqueMember_A693221EA593AB516B3E69FD0E3A1483" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_BrokerPricingMember" xlink:label="loc_ob_BrokerPricingMember_9B6ECE50B4095926F4AB69FD0E3A42F0" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_59D3790D3EC9D1A0D3F969FD0E3AE8E7" xlink:to="loc_ob_BrokerPricingMember_9B6ECE50B4095926F4AB69FD0E3A42F0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StandardPoorsAAPlusRatingMember" xlink:label="loc_us-gaap_StandardPoorsAAPlusRatingMember_D761E2548E61105F86D369FD0E3B3BC1" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_59D3790D3EC9D1A0D3F969FD0E3AE8E7" xlink:to="loc_us-gaap_StandardPoorsAAPlusRatingMember_D761E2548E61105F86D369FD0E3B3BC1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsFairValueDisclosure" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_7543341FF055CDD6CDCD69FD0E3B5630" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems_68B22F20D9A7313BFC5569FD0E3B1D82" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_7543341FF055CDD6CDCD69FD0E3B5630" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsDiscountRate" xlink:label="loc_us-gaap_FairValueInputsDiscountRate_A8624C748F13BD0BA83669FD0E3B8FF7" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems_68B22F20D9A7313BFC5569FD0E3B1D82" xlink:to="loc_us-gaap_FairValueInputsDiscountRate_A8624C748F13BD0BA83669FD0E3B8FF7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLossSeverity" xlink:label="loc_us-gaap_FairValueInputsLossSeverity_21EB92E33D3350F8EAAD69FD0E3B25A2" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems_68B22F20D9A7313BFC5569FD0E3B1D82" xlink:to="loc_us-gaap_FairValueInputsLossSeverity_21EB92E33D3350F8EAAD69FD0E3B25A2" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_NumberOfSecuritiesInEachAssetType" xlink:label="loc_ob_NumberOfSecuritiesInEachAssetType_9D899D756076F8A1535169FD0E3B9417" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems_68B22F20D9A7313BFC5569FD0E3B1D82" xlink:to="loc_ob_NumberOfSecuritiesInEachAssetType_9D899D756076F8A1535169FD0E3B9417" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/InvestmentSecuritiesTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/LegalContingencies" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/LegalContingenciesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LossContingenciesLineItems" xlink:label="loc_us-gaap_LossContingenciesLineItems_E19D78C05B920339A8A2FCADA88F9E18" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LossContingenciesTable" xlink:label="loc_us-gaap_LossContingenciesTable_75E0E62900C0A8EA5D08FCADA88F6BB3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_E19D78C05B920339A8A2FCADA88F9E18" xlink:to="loc_us-gaap_LossContingenciesTable_75E0E62900C0A8EA5D08FCADA88F6BB3" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LitigationStatusAxis" xlink:label="loc_us-gaap_LitigationStatusAxis_FA35936E9EB6AB76B55EFCADA88FD5A7" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_75E0E62900C0A8EA5D08FCADA88F6BB3" xlink:to="loc_us-gaap_LitigationStatusAxis_FA35936E9EB6AB76B55EFCADA88FD5A7" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LitigationStatusDomain" xlink:label="loc_us-gaap_LitigationStatusDomain_19FB781A63E83DF557DBFCADA88F5A25_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LitigationStatusAxis_FA35936E9EB6AB76B55EFCADA88FD5A7" xlink:to="loc_us-gaap_LitigationStatusDomain_19FB781A63E83DF557DBFCADA88F5A25_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LitigationStatusDomain" xlink:label="loc_us-gaap_LitigationStatusDomain_19FB781A63E83DF557DBFCADA88F5A25" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LitigationStatusAxis_FA35936E9EB6AB76B55EFCADA88FD5A7" xlink:to="loc_us-gaap_LitigationStatusDomain_19FB781A63E83DF557DBFCADA88F5A25" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PendingLitigationMember" xlink:label="loc_us-gaap_PendingLitigationMember_A82A36B9CE9C6EF39ABCFCADA88F55C8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LitigationStatusDomain_19FB781A63E83DF557DBFCADA88F5A25" xlink:to="loc_us-gaap_PendingLitigationMember_A82A36B9CE9C6EF39ABCFCADA88F55C8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LitigationCaseAxis" xlink:label="loc_us-gaap_LitigationCaseAxis_8578B79D889B053B71EAFCADA88F3313" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_75E0E62900C0A8EA5D08FCADA88F6BB3" xlink:to="loc_us-gaap_LitigationCaseAxis_8578B79D889B053B71EAFCADA88F3313" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LitigationCaseTypeDomain" xlink:label="loc_us-gaap_LitigationCaseTypeDomain_38CE1C4A2C0D36031664FCADA88F047E_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LitigationCaseAxis_8578B79D889B053B71EAFCADA88F3313" xlink:to="loc_us-gaap_LitigationCaseTypeDomain_38CE1C4A2C0D36031664FCADA88F047E_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LitigationCaseTypeDomain" xlink:label="loc_us-gaap_LitigationCaseTypeDomain_38CE1C4A2C0D36031664FCADA88F047E" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LitigationCaseAxis_8578B79D889B053B71EAFCADA88F3313" xlink:to="loc_us-gaap_LitigationCaseTypeDomain_38CE1C4A2C0D36031664FCADA88F047E" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_TribuneCompanyLitigationMember" xlink:label="loc_ob_TribuneCompanyLitigationMember_271F4CB3CFC3D2D32814FCADA88F0E5C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LitigationCaseTypeDomain_38CE1C4A2C0D36031664FCADA88F047E" xlink:to="loc_ob_TribuneCompanyLitigationMember_271F4CB3CFC3D2D32814FCADA88F0E5C" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ProceedsCommonStockLitigationSettlement" xlink:label="loc_ob_ProceedsCommonStockLitigationSettlement_1F84B7015622AAFDA479FCADA88F0641" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_E19D78C05B920339A8A2FCADA88F9E18" xlink:to="loc_ob_ProceedsCommonStockLitigationSettlement_1F84B7015622AAFDA479FCADA88F0641" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/NatureOfOperationsAndSummaryOfSignificantAccountingPolicies" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetLineItems" xlink:label="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetLineItems_044B9AD0A38A17F34C9FFCADA841AC9C" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTable" xlink:label="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTable_D03959890032C5AE3171FCADA841B565" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetLineItems_044B9AD0A38A17F34C9FFCADA841AC9C" xlink:to="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTable_D03959890032C5AE3171FCADA841B565" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_1D545117372418323C80FCADA841C559" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTable_D03959890032C5AE3171FCADA841B565" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_1D545117372418323C80FCADA841C559" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_AA3EDB748231F39F03B9FCADA841DDD3_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_1D545117372418323C80FCADA841C559" xlink:to="loc_us-gaap_SegmentDomain_AA3EDB748231F39F03B9FCADA841DDD3_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_AA3EDB748231F39F03B9FCADA841DDD3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_1D545117372418323C80FCADA841C559" xlink:to="loc_us-gaap_SegmentDomain_AA3EDB748231F39F03B9FCADA841DDD3" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SpecialtyProductsMember" xlink:label="loc_ob_SpecialtyProductsMember_DB97C2A36CD0BD7548D6FCADA841E878" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_AA3EDB748231F39F03B9FCADA841DDD3" xlink:to="loc_ob_SpecialtyProductsMember_DB97C2A36CD0BD7548D6FCADA841E878" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SpecialtyIndustriesMember" xlink:label="loc_ob_SpecialtyIndustriesMember_4D6804844606B2F40BD5FCADA841636C" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_AA3EDB748231F39F03B9FCADA841DDD3" xlink:to="loc_ob_SpecialtyIndustriesMember_4D6804844606B2F40BD5FCADA841636C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_447D8C2FFEEF4438C067FCADA8418FE9" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTable_D03959890032C5AE3171FCADA841B565" xlink:to="loc_dei_LegalEntityAxis_447D8C2FFEEF4438C067FCADA8418FE9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_6BDACA99E028E0DB8222FCADA841321D_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_447D8C2FFEEF4438C067FCADA8418FE9" xlink:to="loc_dei_EntityDomain_6BDACA99E028E0DB8222FCADA841321D_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_6BDACA99E028E0DB8222FCADA841321D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_447D8C2FFEEF4438C067FCADA8418FE9" xlink:to="loc_dei_EntityDomain_6BDACA99E028E0DB8222FCADA841321D" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_WhiteMountainsInsuranceGroupLtdMember" xlink:label="loc_ob_WhiteMountainsInsuranceGroupLtdMember_1A69DFF6262C7AB05602FCADA84109EE" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_6BDACA99E028E0DB8222FCADA841321D" xlink:to="loc_ob_WhiteMountainsInsuranceGroupLtdMember_1A69DFF6262C7AB05602FCADA84109EE" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ParticipationPercentageInQuotaShareReinsuranceAgreements" xlink:label="loc_ob_ParticipationPercentageInQuotaShareReinsuranceAgreements_50455C0F73745AFD8BC3FCADA841B812" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetLineItems_044B9AD0A38A17F34C9FFCADA841AC9C" xlink:to="loc_ob_ParticipationPercentageInQuotaShareReinsuranceAgreements_50455C0F73745AFD8BC3FCADA841B812" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_D8F14021BECC464ED317FCADA841B174" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetLineItems_044B9AD0A38A17F34C9FFCADA841AC9C" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_D8F14021BECC464ED317FCADA841B174" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NumberOfOperatingSegments" xlink:label="loc_us-gaap_NumberOfOperatingSegments_B9D6E660E6BF321497E7FCADA8414FF0" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetLineItems_044B9AD0A38A17F34C9FFCADA841AC9C" xlink:to="loc_us-gaap_NumberOfOperatingSegments_B9D6E660E6BF321497E7FCADA8414FF0" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentUnamortizedDiscount" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_231B4D9078FB4463E68EFCADA8419790" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetLineItems_044B9AD0A38A17F34C9FFCADA841AC9C" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_231B4D9078FB4463E68EFCADA8419790" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/NatureOfOperationsAndSummaryOfSignificantAccountingPoliciesPolicies" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/Reinsurance" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/ReinsuranceDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRetentionPolicyLineItems" xlink:label="loc_us-gaap_ReinsuranceRetentionPolicyLineItems_288E831DDB71BFEFCDC86F5C23A4ABE9" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRetentionPolicyTable" xlink:label="loc_us-gaap_ReinsuranceRetentionPolicyTable_4726811F47C75AA373A46F5C23A43C54" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyLineItems_288E831DDB71BFEFCDC86F5C23A4ABE9" xlink:to="loc_us-gaap_ReinsuranceRetentionPolicyTable_4726811F47C75AA373A46F5C23A43C54" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CreditRatingStandardPoorsAxis" xlink:label="loc_us-gaap_CreditRatingStandardPoorsAxis_4D8A8B88AA2948D001FB6F5C23A45A4D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyTable_4726811F47C75AA373A46F5C23A43C54" xlink:to="loc_us-gaap_CreditRatingStandardPoorsAxis_4D8A8B88AA2948D001FB6F5C23A45A4D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ExternalCreditRatingStandardPoorsMember" xlink:label="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_4DEFB19AC65783E575046F5C23A46935_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditRatingStandardPoorsAxis_4D8A8B88AA2948D001FB6F5C23A45A4D" xlink:to="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_4DEFB19AC65783E575046F5C23A46935_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ExternalCreditRatingStandardPoorsMember" xlink:label="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_4DEFB19AC65783E575046F5C23A46935" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditRatingStandardPoorsAxis_4D8A8B88AA2948D001FB6F5C23A45A4D" xlink:to="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_4DEFB19AC65783E575046F5C23A46935" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StandardPoorsAARatingMember" xlink:label="loc_us-gaap_StandardPoorsAARatingMember_8EC8445CDA45B337D9226F5C23A4DB16" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_4DEFB19AC65783E575046F5C23A46935" xlink:to="loc_us-gaap_StandardPoorsAARatingMember_8EC8445CDA45B337D9226F5C23A4DB16" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StandardPoorsARatingMember" xlink:label="loc_us-gaap_StandardPoorsARatingMember_0749462175BFB622778D6F5C23A4543A" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_4DEFB19AC65783E575046F5C23A46935" xlink:to="loc_us-gaap_StandardPoorsARatingMember_0749462175BFB622778D6F5C23A4543A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StandardPoorsBBBPlusRatingMember" xlink:label="loc_us-gaap_StandardPoorsBBBPlusRatingMember_E3FFEE37D32DA5A68F766F5C23A498F2" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExternalCreditRatingStandardPoorsMember_4DEFB19AC65783E575046F5C23A46935" xlink:to="loc_us-gaap_StandardPoorsBBBPlusRatingMember_E3FFEE37D32DA5A68F766F5C23A498F2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_EB550C9066BD053F7CA46F5C23A434FE" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyTable_4726811F47C75AA373A46F5C23A43C54" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_EB550C9066BD053F7CA46F5C23A434FE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_589C62D7B7AC27C5F35C6F5C23A4BE75_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_EB550C9066BD053F7CA46F5C23A434FE" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_589C62D7B7AC27C5F35C6F5C23A4BE75_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_589C62D7B7AC27C5F35C6F5C23A4BE75" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_EB550C9066BD053F7CA46F5C23A434FE" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_589C62D7B7AC27C5F35C6F5C23A4BE75" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDiscontinuedOperationsMember" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_51658470F6E5BE7DFDFF6F5C23A45AAB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_589C62D7B7AC27C5F35C6F5C23A4BE75" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_51658470F6E5BE7DFDFF6F5C23A45AAB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis" xlink:label="loc_us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis_43223A9CCFF3D6CF98D56F5C23A4B48F" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyTable_4726811F47C75AA373A46F5C23A43C54" xlink:to="loc_us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis_43223A9CCFF3D6CF98D56F5C23A4B48F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentDomain" xlink:label="loc_us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentDomain_C710E3770908C38417F86F5C23A4392C_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis_43223A9CCFF3D6CF98D56F5C23A4B48F" xlink:to="loc_us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentDomain_C710E3770908C38417F86F5C23A4392C_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentDomain" xlink:label="loc_us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentDomain_C710E3770908C38417F86F5C23A4392C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentAxis_43223A9CCFF3D6CF98D56F5C23A4B48F" xlink:to="loc_us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentDomain_C710E3770908C38417F86F5C23A4392C" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ReinsuranceTypeandTierIdentifierAxis" xlink:label="loc_ob_ReinsuranceTypeandTierIdentifierAxis_97134903930E423E23D56F5C23A4659A" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyTable_4726811F47C75AA373A46F5C23A43C54" xlink:to="loc_ob_ReinsuranceTypeandTierIdentifierAxis_97134903930E423E23D56F5C23A4659A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ReinsuranceTypeandTierIdentifierDomain" xlink:label="loc_ob_ReinsuranceTypeandTierIdentifierDomain_B45AED0DA3F2477F366E6F5C23A4B78F_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ob_ReinsuranceTypeandTierIdentifierAxis_97134903930E423E23D56F5C23A4659A" xlink:to="loc_ob_ReinsuranceTypeandTierIdentifierDomain_B45AED0DA3F2477F366E6F5C23A4B78F_default" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ReinsuranceTypeandTierIdentifierDomain" xlink:label="loc_ob_ReinsuranceTypeandTierIdentifierDomain_B45AED0DA3F2477F366E6F5C23A4B78F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ob_ReinsuranceTypeandTierIdentifierAxis_97134903930E423E23D56F5C23A4659A" xlink:to="loc_ob_ReinsuranceTypeandTierIdentifierDomain_B45AED0DA3F2477F366E6F5C23A4B78F" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_LayerThreeMember" xlink:label="loc_ob_LayerThreeMember_D8D8B200254ACD5C87EC6F5C23A4EEFB" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_ReinsuranceTypeandTierIdentifierDomain_B45AED0DA3F2477F366E6F5C23A4B78F" xlink:to="loc_ob_LayerThreeMember_D8D8B200254ACD5C87EC6F5C23A4EEFB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsurancePolicyTypeAxis" xlink:label="loc_us-gaap_ReinsurancePolicyTypeAxis_BAC759B0F1988EB5142B6F5C23A4E819" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyTable_4726811F47C75AA373A46F5C23A43C54" xlink:to="loc_us-gaap_ReinsurancePolicyTypeAxis_BAC759B0F1988EB5142B6F5C23A4E819" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsurancePolicyDomain" xlink:label="loc_us-gaap_ReinsurancePolicyDomain_37CE414E1A33769FF4AF6F5C23A4595A_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReinsurancePolicyTypeAxis_BAC759B0F1988EB5142B6F5C23A4E819" xlink:to="loc_us-gaap_ReinsurancePolicyDomain_37CE414E1A33769FF4AF6F5C23A4595A_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsurancePolicyDomain" xlink:label="loc_us-gaap_ReinsurancePolicyDomain_37CE414E1A33769FF4AF6F5C23A4595A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReinsurancePolicyTypeAxis_BAC759B0F1988EB5142B6F5C23A4E819" xlink:to="loc_us-gaap_ReinsurancePolicyDomain_37CE414E1A33769FF4AF6F5C23A4595A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PropertyCatastropheReinsuranceMember" xlink:label="loc_ob_PropertyCatastropheReinsuranceMember_1807009F8E17F13C122E6F5C23A4687B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsurancePolicyDomain_37CE414E1A33769FF4AF6F5C23A4595A" xlink:to="loc_ob_PropertyCatastropheReinsuranceMember_1807009F8E17F13C122E6F5C23A4687B" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_PropertyPerRiskReinsuranceProgramMember" xlink:label="loc_ob_PropertyPerRiskReinsuranceProgramMember_17828C144E17DF319A646F5C23A40F0B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsurancePolicyDomain_37CE414E1A33769FF4AF6F5C23A4595A" xlink:to="loc_ob_PropertyPerRiskReinsuranceProgramMember_17828C144E17DF319A646F5C23A40F0B" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_MPCIPortfolioMember" xlink:label="loc_ob_MPCIPortfolioMember_3C14E985A42F69FCB75A6F5C3FFA128B" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsurancePolicyDomain_37CE414E1A33769FF4AF6F5C23A4595A" xlink:to="loc_ob_MPCIPortfolioMember_3C14E985A42F69FCB75A6F5C3FFA128B" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CropHailPortfolioMember" xlink:label="loc_ob_CropHailPortfolioMember_C9111D8B52102971B94F6F5D24A02968" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsurancePolicyDomain_37CE414E1A33769FF4AF6F5C23A4595A" xlink:to="loc_ob_CropHailPortfolioMember_C9111D8B52102971B94F6F5D24A02968" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CreditRatingAMBestAxis" xlink:label="loc_us-gaap_CreditRatingAMBestAxis_A47B44D341F3899266AB6F5C23A4A9C1" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyTable_4726811F47C75AA373A46F5C23A43C54" xlink:to="loc_us-gaap_CreditRatingAMBestAxis_A47B44D341F3899266AB6F5C23A4A9C1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CreditRatingAMBestDomain" xlink:label="loc_us-gaap_CreditRatingAMBestDomain_5EE0129A7B2CEC8B771E6F5C23A43687_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditRatingAMBestAxis_A47B44D341F3899266AB6F5C23A4A9C1" xlink:to="loc_us-gaap_CreditRatingAMBestDomain_5EE0129A7B2CEC8B771E6F5C23A43687_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CreditRatingAMBestDomain" xlink:label="loc_us-gaap_CreditRatingAMBestDomain_5EE0129A7B2CEC8B771E6F5C23A43687" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditRatingAMBestAxis_A47B44D341F3899266AB6F5C23A4A9C1" xlink:to="loc_us-gaap_CreditRatingAMBestDomain_5EE0129A7B2CEC8B771E6F5C23A43687" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_719D53C61D9379A5352D6F5C23A41A21" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyTable_4726811F47C75AA373A46F5C23A43C54" xlink:to="loc_us-gaap_RangeAxis_719D53C61D9379A5352D6F5C23A41A21" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_11D95A7DEB344EAA55716F5C23A4D04A_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_719D53C61D9379A5352D6F5C23A41A21" xlink:to="loc_us-gaap_RangeMember_11D95A7DEB344EAA55716F5C23A4D04A_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_11D95A7DEB344EAA55716F5C23A4D04A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_719D53C61D9379A5352D6F5C23A41A21" xlink:to="loc_us-gaap_RangeMember_11D95A7DEB344EAA55716F5C23A4D04A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_1CEC19DD11CA5242604C6F5C23A43393" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_11D95A7DEB344EAA55716F5C23A4D04A" xlink:to="loc_us-gaap_MinimumMember_1CEC19DD11CA5242604C6F5C23A43393" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_ADF23FFE5884400F57536F5C23A4132B" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_11D95A7DEB344EAA55716F5C23A4D04A" xlink:to="loc_us-gaap_MaximumMember_ADF23FFE5884400F57536F5C23A4132B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRetentionPolicyAmountRetained" xlink:label="loc_us-gaap_ReinsuranceRetentionPolicyAmountRetained_02AAD046FF845E9811F06F5C23A4D540" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyLineItems_288E831DDB71BFEFCDC86F5C23A4ABE9" xlink:to="loc_us-gaap_ReinsuranceRetentionPolicyAmountRetained_02AAD046FF845E9811F06F5C23A4D540" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRetentionPolicyExcessRetentionAmountReinsured" xlink:label="loc_us-gaap_ReinsuranceRetentionPolicyExcessRetentionAmountReinsured_D4FA20D47D3ADF814C116F5C23B4E759" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyLineItems_288E831DDB71BFEFCDC86F5C23A4ABE9" xlink:to="loc_us-gaap_ReinsuranceRetentionPolicyExcessRetentionAmountReinsured_D4FA20D47D3ADF814C116F5C23B4E759" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_CoverageinExcessofRetainedAmount" xlink:label="loc_ob_CoverageinExcessofRetainedAmount_B2B8CEFE886BB000D5846F5C3F5EAB89" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyLineItems_288E831DDB71BFEFCDC86F5C23A4ABE9" xlink:to="loc_ob_CoverageinExcessofRetainedAmount_B2B8CEFE886BB000D5846F5C3F5EAB89" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RetainedLosses" xlink:label="loc_ob_RetainedLosses_54030B0638692F8A964E6F5CC541EED9" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyLineItems_288E831DDB71BFEFCDC86F5C23A4ABE9" xlink:to="loc_ob_RetainedLosses_54030B0638692F8A964E6F5CC541EED9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceReceivablesPaidLossesRecoverable" xlink:label="loc_us-gaap_ReinsuranceReceivablesPaidLossesRecoverable_B9D99AA028DD48965E2E6F5C23B4C980" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyLineItems_288E831DDB71BFEFCDC86F5C23A4ABE9" xlink:to="loc_us-gaap_ReinsuranceReceivablesPaidLossesRecoverable_B9D99AA028DD48965E2E6F5C23B4C980" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims" xlink:label="loc_us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims_E7DFDA58E0DFB030A8B46F5C23B4B05F" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyLineItems_288E831DDB71BFEFCDC86F5C23A4ABE9" xlink:to="loc_us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims_E7DFDA58E0DFB030A8B46F5C23B4B05F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRecoverables" xlink:label="loc_us-gaap_ReinsuranceRecoverables_40A06B898C08728AB6096F5C23B450D5" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyLineItems_288E831DDB71BFEFCDC86F5C23A4ABE9" xlink:to="loc_us-gaap_ReinsuranceRecoverables_40A06B898C08728AB6096F5C23B450D5" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRecoverablesPercentageOfTotal" xlink:label="loc_us-gaap_ReinsuranceRecoverablesPercentageOfTotal_3D53CF3C20A6CC040F8D6F5C23B47BC6" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyLineItems_288E831DDB71BFEFCDC86F5C23A4ABE9" xlink:to="loc_us-gaap_ReinsuranceRecoverablesPercentageOfTotal_3D53CF3C20A6CC040F8D6F5C23B47BC6" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_AmBestRatingSystemNumberOfRatings" xlink:label="loc_ob_AmBestRatingSystemNumberOfRatings_3799FB37E20BBABED91A6F5C23B47696" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReinsuranceRetentionPolicyLineItems_288E831DDB71BFEFCDC86F5C23A4ABE9" xlink:to="loc_ob_AmBestRatingSystemNumberOfRatings_3799FB37E20BBABED91A6F5C23B47696" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/ReinsuranceTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/RetirementPlans" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/RetirementPlansPeriodicBenefitCostDetails" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/RetirementPlansTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/SegmentInformation" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/SegmentInformationDetails" xlink:type="extended">
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:type="locator" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_FA759FC6A42C6A81C13B69FD0DFC39E3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_FA759FC6A42C6A81C13B69FD0DFC39E3" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_6EBDEFB0713F8D1B2E5C69FD0DFC2D10" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_FA759FC6A42C6A81C13B69FD0DFC39E3" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_6EBDEFB0713F8D1B2E5C69FD0DFC2D10" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_A05D8B927B8CB035B5F369FD0DFC2F6F_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_6EBDEFB0713F8D1B2E5C69FD0DFC2D10" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_A05D8B927B8CB035B5F369FD0DFC2F6F_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentOperatingActivitiesDomain" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_A05D8B927B8CB035B5F369FD0DFC2F6F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_6EBDEFB0713F8D1B2E5C69FD0DFC2D10" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_A05D8B927B8CB035B5F369FD0DFC2F6F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDiscontinuedOperationsMember" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_6DCFA67313441EEBF4F769FD0DFD444B" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_A05D8B927B8CB035B5F369FD0DFC2F6F" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_6DCFA67313441EEBF4F769FD0DFD444B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_LegalEntityAxis" xlink:label="loc_dei_LegalEntityAxis_39BE8C411AFE0E2D392369FD0DFDFAD9" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_FA759FC6A42C6A81C13B69FD0DFC39E3" xlink:to="loc_dei_LegalEntityAxis_39BE8C411AFE0E2D392369FD0DFDFAD9" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_633EAC9F6ED418F51E8869FD0DFD2D8C_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_39BE8C411AFE0E2D392369FD0DFDFAD9" xlink:to="loc_dei_EntityDomain_633EAC9F6ED418F51E8869FD0DFD2D8C_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityDomain" xlink:label="loc_dei_EntityDomain_633EAC9F6ED418F51E8869FD0DFD2D8C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_39BE8C411AFE0E2D392369FD0DFDFAD9" xlink:to="loc_dei_EntityDomain_633EAC9F6ED418F51E8869FD0DFD2D8C" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RunoffMember" xlink:label="loc_ob_RunoffMember_C10B2ABACA74CD9A82D369FD0DFDA6B8" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_633EAC9F6ED418F51E8869FD0DFD2D8C" xlink:to="loc_ob_RunoffMember_C10B2ABACA74CD9A82D369FD0DFDA6B8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_4686B8F2AEEF7045E33969FD0DFD5BFE" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_FA759FC6A42C6A81C13B69FD0DFC39E3" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_4686B8F2AEEF7045E33969FD0DFD5BFE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_42662F86002F8DC25F9969FD0DFDA367_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_4686B8F2AEEF7045E33969FD0DFD5BFE" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_42662F86002F8DC25F9969FD0DFDA367_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain" xlink:label="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_42662F86002F8DC25F9969FD0DFDA367" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis_4686B8F2AEEF7045E33969FD0DFD5BFE" xlink:to="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_42662F86002F8DC25F9969FD0DFDA367" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FixedMaturitiesMember" xlink:label="loc_us-gaap_FixedMaturitiesMember_F3F1E41F04AC734D966269FD0DFDBD5D" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MajorTypesOfDebtAndEquitySecuritiesDomain_42662F86002F8DC25F9969FD0DFDA367" xlink:to="loc_us-gaap_FixedMaturitiesMember_F3F1E41F04AC734D966269FD0DFDBD5D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_52A09E23CDE481BB398569FD0DFDD626" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_FA759FC6A42C6A81C13B69FD0DFC39E3" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_52A09E23CDE481BB398569FD0DFDD626" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_8F4F64114A49088EBC7469FD0DFDF569_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_52A09E23CDE481BB398569FD0DFDD626" xlink:to="loc_us-gaap_SegmentDomain_8F4F64114A49088EBC7469FD0DFDF569_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_8F4F64114A49088EBC7469FD0DFDF569" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_52A09E23CDE481BB398569FD0DFDD626" xlink:to="loc_us-gaap_SegmentDomain_8F4F64114A49088EBC7469FD0DFDF569" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SpecialtyProductsMember" xlink:label="loc_ob_SpecialtyProductsMember_3AA83B8F3FB8076FEDB269FD0DFDBA14" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8F4F64114A49088EBC7469FD0DFDF569" xlink:to="loc_ob_SpecialtyProductsMember_3AA83B8F3FB8076FEDB269FD0DFDBA14" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_SpecialtyIndustriesMember" xlink:label="loc_ob_SpecialtyIndustriesMember_5A5F90B38047ED41A22869FD0DFD995D" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8F4F64114A49088EBC7469FD0DFDF569" xlink:to="loc_ob_SpecialtyIndustriesMember_5A5F90B38047ED41A22869FD0DFD995D" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InvestingFinancingAndCorporateOperationsMember" xlink:label="loc_ob_InvestingFinancingAndCorporateOperationsMember_929E1A15847A0F0C671169FD0DFD1B52" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_8F4F64114A49088EBC7469FD0DFDF569" xlink:to="loc_ob_InvestingFinancingAndCorporateOperationsMember_929E1A15847A0F0C671169FD0DFD1B52" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_NumberOfMajorUnderwritingUnits" xlink:label="loc_ob_NumberOfMajorUnderwritingUnits_F9CDA0EF02D66F4EBBDC69FD0DFEC48F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_ob_NumberOfMajorUnderwritingUnits_F9CDA0EF02D66F4EBBDC69FD0DFEC48F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PremiumsWrittenNet" xlink:label="loc_us-gaap_PremiumsWrittenNet_AE5F1563F878840F479B69FD0DFEABB4" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_PremiumsWrittenNet_AE5F1563F878840F479B69FD0DFEABB4" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_FixedMaturitiesInvestmentsTradingSecuritiesDebtReclassifiedtoAssetsHeldforsale" xlink:label="loc_ob_FixedMaturitiesInvestmentsTradingSecuritiesDebtReclassifiedtoAssetsHeldforsale_0568A72D07001838616869FD0DFED5BE" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_ob_FixedMaturitiesInvestmentsTradingSecuritiesDebtReclassifiedtoAssetsHeldforsale_0568A72D07001838616869FD0DFED5BE" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PremiumsEarnedNet" xlink:label="loc_us-gaap_PremiumsEarnedNet_CD20A521CAB06B1D9C6A69FD0DFEF872" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_PremiumsEarnedNet_CD20A521CAB06B1D9C6A69FD0DFEF872" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PolicyholderBenefitsAndClaimsIncurredNet" xlink:label="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_92B37039B99E174C054B69FD0DFE35A1" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_PolicyholderBenefitsAndClaimsIncurredNet_92B37039B99E174C054B69FD0DFE35A1" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_InsuranceAndReinsuranceAcquisitionExpenses" xlink:label="loc_ob_InsuranceAndReinsuranceAcquisitionExpenses_FC83A5C788133EDAFDBD69FD0DFE99CC" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_ob_InsuranceAndReinsuranceAcquisitionExpenses_FC83A5C788133EDAFDBD69FD0DFE99CC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherUnderwritingExpense" xlink:label="loc_us-gaap_OtherUnderwritingExpense_FBE371302FA7D12E951E69FD0DFE2721" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_OtherUnderwritingExpense_FBE371302FA7D12E951E69FD0DFE2721" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_UnderwritingIncomeLoss" xlink:label="loc_us-gaap_UnderwritingIncomeLoss_F6C5303E055F339BC3BE69FD0DFE0FBC" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_UnderwritingIncomeLoss_F6C5303E055F339BC3BE69FD0DFE0FBC" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetInvestmentIncome" xlink:label="loc_us-gaap_NetInvestmentIncome_50FFBD554FD8D37C9C3769FD0DFE7D39" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_NetInvestmentIncome_50FFBD554FD8D37C9C3769FD0DFE7D39" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GainLossOnInvestments" xlink:label="loc_us-gaap_GainLossOnInvestments_731626332002F79A308469FD0DFE1006" xlink:type="locator" />
    <definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_GainLossOnInvestments_731626332002F79A308469FD0DFE1006" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_3FA5CC10FEF860AFAD1569FD0DFE4F2D" xlink:type="locator" />
    <definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_3FA5CC10FEF860AFAD1569FD0DFE4F2D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_205503CE8A2DDB41071369FD0DFE9E5A" xlink:type="locator" />
    <definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_205503CE8A2DDB41071369FD0DFE9E5A" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestExpenseDebt" xlink:label="loc_us-gaap_InterestExpenseDebt_2AF3B029F322E4D42B3569FD0DFE2842" xlink:type="locator" />
    <definitionArc order="13" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_InterestExpenseDebt_2AF3B029F322E4D42B3569FD0DFE2842" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_33374DCAB0138F63E2FA69FD0DFF2F6D" xlink:type="locator" />
    <definitionArc order="14" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_33374DCAB0138F63E2FA69FD0DFF2F6D" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SegmentReportingInformationAdditionalInformationAbstract" xlink:label="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_B2F52F3D4F8170AC73A569FD0DFFF321" xlink:type="locator" />
    <definitionArc order="15" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_B2F52F3D4F8170AC73A569FD0DFFF321" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Investments" xlink:label="loc_us-gaap_Investments_B0BB754A6BC77C517C3A69FD0DFF963F" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_B2F52F3D4F8170AC73A569FD0DFFF321" xlink:to="loc_us-gaap_Investments_B0BB754A6BC77C517C3A69FD0DFF963F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceRecoverables" xlink:label="loc_us-gaap_ReinsuranceRecoverables_90587B44E19962BA85B069FD0DFF9F44" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_B2F52F3D4F8170AC73A569FD0DFFF321" xlink:to="loc_us-gaap_ReinsuranceRecoverables_90587B44E19962BA85B069FD0DFF9F44" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredPolicyAcquisitionCosts" xlink:label="loc_us-gaap_DeferredPolicyAcquisitionCosts_ACC302E94833F2D8CCA869FD0DFF46ED" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_B2F52F3D4F8170AC73A569FD0DFFF321" xlink:to="loc_us-gaap_DeferredPolicyAcquisitionCosts_ACC302E94833F2D8CCA869FD0DFF46ED" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_D3A1826310763F4D0E4869FD0DFFA1DB" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_B2F52F3D4F8170AC73A569FD0DFFF321" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_D3A1826310763F4D0E4869FD0DFFA1DB" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_UnearnedPremiums" xlink:label="loc_us-gaap_UnearnedPremiums_EE4468029E9D5ED40B4469FD0DFFF2F1" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_B2F52F3D4F8170AC73A569FD0DFFF321" xlink:to="loc_us-gaap_UnearnedPremiums_EE4468029E9D5ED40B4469FD0DFFF2F1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebt" xlink:label="loc_us-gaap_LongTermDebt_E28D80EF19E9C0776ED869FD0DFF6522" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_B2F52F3D4F8170AC73A569FD0DFFF321" xlink:to="loc_us-gaap_LongTermDebt_E28D80EF19E9C0776ED869FD0DFF6522" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_LossandLAERatio" xlink:label="loc_ob_LossandLAERatio_8923FA630D484BA48D1C69FD0DFF6A4F" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_B2F52F3D4F8170AC73A569FD0DFFF321" xlink:to="loc_ob_LossandLAERatio_8923FA630D484BA48D1C69FD0DFF6A4F" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_ExpenseRatio" xlink:label="loc_ob_ExpenseRatio_8ED764438BA696F32E1D69FD0DFFE577" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_B2F52F3D4F8170AC73A569FD0DFFF321" xlink:to="loc_ob_ExpenseRatio_8ED764438BA696F32E1D69FD0DFFE577" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CombinedRatio" xlink:label="loc_us-gaap_CombinedRatio_F97ADD2B94C56056D40469FD0DFFECA8" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationAdditionalInformationAbstract_B2F52F3D4F8170AC73A569FD0DFFF321" xlink:to="loc_us-gaap_CombinedRatio_F97ADD2B94C56056D40469FD0DFFECA8" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NumberOfOperatingSegments" xlink:label="loc_us-gaap_NumberOfOperatingSegments_C48EFC391DA0668AD83369FD0DFFA714" xlink:type="locator" />
    <definitionArc order="16" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_B047E4F29D4CDF13C53F69FD0DFE521F" xlink:to="loc_us-gaap_NumberOfOperatingSegments_C48EFC391DA0668AD83369FD0DFFA714" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/SegmentInformationTables" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/UnpaidLossAndLossAdjustmentExpenseLaeReserves" xlink:type="extended" />
  <definitionLink xlink:role="http://www.onebeacon.com/role/UnpaidLossAndLossAdjustmentExpenseLaeReservesDetails" xlink:type="extended">
    <loc xlink:href="ob-20140630.xsd#ob_LossAndLossAdjustmentExpenseLineItems" xlink:label="loc_ob_LossAndLossAdjustmentExpenseLineItems_EF0A9ED7F0599D6041A769FD0EA5D050" xlink:type="locator" />
    <loc xlink:href="ob-20140630.xsd#ob_LossAndLossAdjustmentExpenseReservesTable" xlink:label="loc_ob_LossAndLossAdjustmentExpenseReservesTable_954D9C737FE57F8DFEFB69FD0EA46FCD" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_ob_LossAndLossAdjustmentExpenseLineItems_EF0A9ED7F0599D6041A769FD0EA5D050" xlink:to="loc_ob_LossAndLossAdjustmentExpenseReservesTable_954D9C737FE57F8DFEFB69FD0EA46FCD" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_40BFB4B8B34077A7CA7469FD0EA5A9B2" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_ob_LossAndLossAdjustmentExpenseReservesTable_954D9C737FE57F8DFEFB69FD0EA46FCD" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_40BFB4B8B34077A7CA7469FD0EA5A9B2" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_44626194BB030E24773569FD0EA5CF9A_default" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_40BFB4B8B34077A7CA7469FD0EA5A9B2" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_44626194BB030E24773569FD0EA5CF9A_default" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_44626194BB030E24773569FD0EA5CF9A" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_40BFB4B8B34077A7CA7469FD0EA5A9B2" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_44626194BB030E24773569FD0EA5CF9A" xlink:type="arc" />
    <loc xlink:href="ob-20140630.xsd#ob_RunoffMember" xlink:label="loc_ob_RunoffMember_87B92366674B610BCE6969FD0EA5C423" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_44626194BB030E24773569FD0EA5CF9A" xlink:to="loc_ob_RunoffMember_87B92366674B610BCE6969FD0EA5C423" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_BFE7F50E55F107E05DDA69FD0EA57E3C" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ob_LossAndLossAdjustmentExpenseLineItems_EF0A9ED7F0599D6041A769FD0EA5D050" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_BFE7F50E55F107E05DDA69FD0EA57E3C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense" xlink:label="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_14CCAD98FB904C681D5C69FD0EA526C3" xlink:type="locator" />
    <definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_BFE7F50E55F107E05DDA69FD0EA57E3C" xlink:to="loc_us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_14CCAD98FB904C681D5C69FD0EA526C3" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims" xlink:label="loc_us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims_FB3FBD533EDE5AAC5A5369FD0EA585CA" xlink:type="locator" />
    <definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_BFE7F50E55F107E05DDA69FD0EA57E3C" xlink:to="loc_us-gaap_ReinsuranceReceivablesIncurredButNotReportedClaims_FB3FBD533EDE5AAC5A5369FD0EA585CA" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsCurrentYear" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsCurrentYear_E1A50644DE32EFAFD85269FD0EA5974C" xlink:type="locator" />
    <definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_BFE7F50E55F107E05DDA69FD0EA57E3C" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsCurrentYear_E1A50644DE32EFAFD85269FD0EA5974C" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsPriorYears" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsPriorYears_68A7C8E28DF196F8359769FD0EA5797F" xlink:type="locator" />
    <definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_BFE7F50E55F107E05DDA69FD0EA57E3C" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsPriorYears_68A7C8E28DF196F8359769FD0EA5797F" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims_64C314B381FB4FB46F8E69FD0EA5064E" xlink:type="locator" />
    <definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_BFE7F50E55F107E05DDA69FD0EA57E3C" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims_64C314B381FB4FB46F8E69FD0EA5064E" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear_CCC7DAB0988CCCC0443A69FD0EA603F1" xlink:type="locator" />
    <definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_BFE7F50E55F107E05DDA69FD0EA57E3C" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear_CCC7DAB0988CCCC0443A69FD0EA603F1" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears_BF2CE211AFACD9FC04D969FD0EA6730B" xlink:type="locator" />
    <definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_BFE7F50E55F107E05DDA69FD0EA57E3C" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears_BF2CE211AFACD9FC04D969FD0EA6730B" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid_C4529C2187B7A042707D69FD0EA68733" xlink:type="locator" />
    <definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_BFE7F50E55F107E05DDA69FD0EA57E3C" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaid_C4529C2187B7A042707D69FD0EA68733" xlink:type="arc" />
    <loc xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet" xlink:label="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet_E5A27735E3A0ECCA09DD69FD0EA637A5" xlink:type="locator" />
    <definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNetAbstract_BFE7F50E55F107E05DDA69FD0EA57E3C" xlink:to="loc_us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet_E5A27735E3A0ECCA09DD69FD0EA637A5" xlink:type="arc" />
  </definitionLink>
  <definitionLink xlink:role="http://www.onebeacon.com/role/UnpaidLossAndLossAdjustmentExpenseLaeReservesTables" xlink:type="extended" />
</linkbase>


