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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureEstimatedUsefulLivesOfAssets" id="DisclosureEstimatedUsefulLivesOfAssets">
        <link:definition>1052 - Disclosure - Estimated Useful Lives of Assets (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureReconciliationOfNumberOfSharesUsedInComputationOfBasicAndDilutedNetIncomePerOrdinaryShare" id="DisclosureReconciliationOfNumberOfSharesUsedInComputationOfBasicAndDilutedNetIncomePerOrdinaryShare">
        <link:definition>1053 - Disclosure - Reconciliation of Number of Shares Used in Computation of Basic and Diluted Net Income Per Ordinary Share (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureCostAndFairValueOfInvestments" id="DisclosureCostAndFairValueOfInvestments">
        <link:definition>1054 - Disclosure - Cost and Fair Value of Investments (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureShortTeamInvestmentsAvailableForSaleAdditionalInformation" id="DisclosureShortTeamInvestmentsAvailableForSaleAdditionalInformation">
        <link:definition>1055 - Disclosure - Short Team Investments - Available for Sale - Additional Information (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureAvailableForSaleShortTermInvestmentsByMajorSecurityType" id="DisclosureAvailableForSaleShortTermInvestmentsByMajorSecurityType">
        <link:definition>1056 - Disclosure - Available For Sale Short Term Investments by Major Security Type (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureGoodwill" id="DisclosureGoodwill">
        <link:definition>1057 - Disclosure - Goodwill (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureGoodwillAdditionalInformation" id="DisclosureGoodwillAdditionalInformation">
        <link:definition>1058 - Disclosure - Goodwill - Additional Information (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfClinicalResearchManagementInc" id="DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfClinicalResearchManagementInc">
        <link:definition>1059 - Disclosure - Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed of Clinical Research Management, Inc. (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfClinicalResearchManagementIncParenthetical" id="DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfClinicalResearchManagementIncParenthetical">
        <link:definition>1060 - Disclosure - Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed of Clinical Research Management, Inc. (Parenthetical) (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureProformaEffectInNetRevenueNetIncomeAndEarningsPerShare" id="DisclosureProformaEffectInNetRevenueNetIncomeAndEarningsPerShare">
        <link:definition>1061 - Disclosure - Proforma Effect in Net Revenue, Net Income and Earnings Per Share (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfPMG" id="DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfPMG">
        <link:definition>1062 - Disclosure - Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed of PMG (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfPMGParenthetical" id="DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfPMGParenthetical">
        <link:definition>1063 - Disclosure - Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed of PMG (Parenthetical) (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfMediMediaPharmaSolutions" id="DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfMediMediaPharmaSolutions">
        <link:definition>1064 - Disclosure - Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed of MediMedia Pharma Solutions (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfMediMediaPharmaSolutionsParenthetical" id="DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfMediMediaPharmaSolutionsParenthetical">
        <link:definition>1065 - Disclosure - Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed of MediMedia Pharma Solutions (Parenthetical) (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfAptivSolutions" id="DisclosureSummaryOfEstimatesOfFairValuesOfAssetsAcquiredAndLiabilitiesAssumedOfAptivSolutions">
        <link:definition>1066 - Disclosure - Summary of Estimates of Fair Values of Assets Acquired and Liabilities Assumed of Aptiv Solutions (Detail)</link:definition>
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      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureIntangibleAssets" id="DisclosureIntangibleAssets">
        <link:definition>1067 - Disclosure - Intangible Assets (Detail)</link:definition>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureIntangibleAssetsAdditionalInformation" id="DisclosureIntangibleAssetsAdditionalInformation">
        <link:definition>1068 - Disclosure - Intangible Assets - Additional Information (Detail)</link:definition>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureFutureIntangibleAssetAmortizationExpense" id="DisclosureFutureIntangibleAssetAmortizationExpense">
        <link:definition>1069 - Disclosure - Future Intangible Asset Amortization Expense (Detail)</link:definition>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosurePropertyPlantAndEquipmentNet" id="DisclosurePropertyPlantAndEquipmentNet">
        <link:definition>1070 - Disclosure - Property, Plant and Equipment, Net (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureOtherLiabilities" id="DisclosureOtherLiabilities">
        <link:definition>1071 - Disclosure - Other Liabilities (Detail)</link:definition>
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        <link:definition>1072 - Disclosure - Other Non-Current Liabilities (Detail)</link:definition>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureOtherNonCurrentLiabilitiesParenthetical" id="DisclosureOtherNonCurrentLiabilitiesParenthetical">
        <link:definition>1073 - Disclosure - Other Non-Current Liabilities (Parenthetical) (Detail)</link:definition>
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      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureEmployeeBenefitsAdditionalInformation" id="DisclosureEmployeeBenefitsAdditionalInformation">
        <link:definition>1074 - Disclosure - Employee Benefits - Additional Information (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureChangeInBenefitObligations" id="DisclosureChangeInBenefitObligations">
        <link:definition>1075 - Disclosure - Change in Benefit Obligations (Detail)</link:definition>
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      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureChangeInPlanAssets" id="DisclosureChangeInPlanAssets">
        <link:definition>1076 - Disclosure - Change in Plan Assets (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureFundedStatusUnitedKingdom" id="DisclosureFundedStatusUnitedKingdom">
        <link:definition>1077 - Disclosure - Funded Status - United Kingdom (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureComponentsOfNetPeriodicBenefitCost" id="DisclosureComponentsOfNetPeriodicBenefitCost">
        <link:definition>1078 - Disclosure - Components of Net Periodic Benefit Cost (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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        <link:definition>1079 - Disclosure - Net Periodic Pension Benefit Cost Assumptions (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureAmountsRecognizedInAccumulatedOtherComprehensiveIncomeThatHaveNotBeenRecognized" id="DisclosureAmountsRecognizedInAccumulatedOtherComprehensiveIncomeThatHaveNotBeenRecognized">
        <link:definition>1080 - Disclosure - Amounts recognized in accumulated other comprehensive income that have not been recognized (Detail)</link:definition>
        <link:usedOn>link:calculationLink</link:usedOn>
        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureAssumptionsUsedInDeterminingBenefitObligation" id="DisclosureAssumptionsUsedInDeterminingBenefitObligation">
        <link:definition>1081 - Disclosure - Assumptions Used in Determining Benefit Obligation (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureExpectedLongTermRatesOfReturnOnDifferentAssetClasses" id="DisclosureExpectedLongTermRatesOfReturnOnDifferentAssetClasses">
        <link:definition>1082 - Disclosure - Expected Long Term Rates of Return on Different Asset Classes (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureActualPlanAssetAllocation" id="DisclosureActualPlanAssetAllocation">
        <link:definition>1083 - Disclosure - Actual Plan Asset Allocation (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosurePlanAssetFairValueMeasurements" id="DisclosurePlanAssetFairValueMeasurements">
        <link:definition>1084 - Disclosure - Plan Asset Fair Value Measurements (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureAnnualBenefitPayments" id="DisclosureAnnualBenefitPayments">
        <link:definition>1085 - Disclosure - Annual Benefit Payments (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureFundedStatusSwitzerland" id="DisclosureFundedStatusSwitzerland">
        <link:definition>1086 - Disclosure - Funded Status - Switzerland (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureEquityIncentiveSchemesAndStockCompensationChargesAdditionalInformation" id="DisclosureEquityIncentiveSchemesAndStockCompensationChargesAdditionalInformation">
        <link:definition>1087 - Disclosure - Equity Incentive Schemes and Stock Compensation Charges - Additional Information (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureSummaryOfStockOptionActivity" id="DisclosureSummaryOfStockOptionActivity">
        <link:definition>1088 - Disclosure - Summary of Stock Option Activity (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureSummaryOfMovementInNonVestedShareOptions" id="DisclosureSummaryOfMovementInNonVestedShareOptions">
        <link:definition>1089 - Disclosure - Summary of Movement in Non-Vested Share Options (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureOutstandingAndExercisableShareOptions" id="DisclosureOutstandingAndExercisableShareOptions">
        <link:definition>1090 - Disclosure - Outstanding and Exercisable Share Options (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
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        <link:definition>1091 - Disclosure - Schedule of Weighted Average Fair Values and Assumptions Used (Detail)</link:definition>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureSummaryOfRSUAndPSUActivity" id="DisclosureSummaryOfRSUAndPSUActivity">
        <link:definition>1092 - Disclosure - Summary of RSU and PSU Activity (Detail)</link:definition>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureScheduleOfNoncashStockCompensationExpense" id="DisclosureScheduleOfNoncashStockCompensationExpense">
        <link:definition>1093 - Disclosure - Schedule of Non-cash Stock Compensation Expense (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
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      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureGovernmentGrants" id="DisclosureGovernmentGrants">
        <link:definition>1094 - Disclosure - Government Grants (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
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        <link:definition>1095 - Disclosure - Government Grants - Additional Information (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureShareCapitalAdditionalInformation" id="DisclosureShareCapitalAdditionalInformation">
        <link:definition>1096 - Disclosure - Share Capital - Additional Information (Detail)</link:definition>
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        <link:definition>1097 - Disclosure - Components of Income Before Provision for Income Taxes (Detail)</link:definition>
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        <link:definition>1098 - Disclosure - Components of Provision for Income Taxes (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
      </link:roleType>
      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureIncomeTaxesAdditionalInformation" id="DisclosureIncomeTaxesAdditionalInformation">
        <link:definition>1099 - Disclosure - Income Taxes - Additional Information (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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        <link:definition>1100 - Disclosure - Consolidated Reported Provision for Income Taxes Differed from Statutory Rate (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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        <link:definition>1101 - Disclosure - Consolidated Reported Provision for Income Taxes Differed from Statutory Rate (Parenthetical) (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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        <link:definition>1102 - Disclosure - Tax Effects of Temporary Differences That Gives Rise to Significant Portions of Deferred Tax Assets and Liabilities (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
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        <link:definition>1103 - Disclosure - Expected Expiry Dates of NOI's (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureRecognizedRestructuringAndOtherItemsNet" id="DisclosureRecognizedRestructuringAndOtherItemsNet">
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureRestructuringCharges" id="DisclosureRestructuringCharges">
        <link:definition>1107 - Disclosure - Restructuring Charges (Detail)</link:definition>
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        <link:definition>1108 - Disclosure - Provision for Doubtful Debts (Detail)</link:definition>
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        <link:definition>1109 - Disclosure - Commitments and Contingencies - Additional Information (Detail)</link:definition>
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        <link:definition>1112 - Disclosure - Distribution of Income from operations, including Restructuring, by Geographical Area (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
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        <link:usedOn>link:presentationLink</link:usedOn>
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        <link:definition>1118 - Disclosure - Clients Representing Company's Net Revenue (Detail)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
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      <link:roleType roleURI="http://www.iconclinical.com/taxonomy/role/DisclosureDistributionOfInterestIncomeByGeographicalArea" id="DisclosureDistributionOfInterestIncomeByGeographicalArea">
        <link:definition>1119 - Disclosure - Distribution of Interest Income by Geographical Area (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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        <link:definition>1120 - Disclosure - Distribution of Income Tax Charge by Geographical Area (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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        <link:definition>1121 - Disclosure - Supplemental Disclosure of Cash Flow Information (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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        <link:definition>1122 - Disclosure - Accumulated Other Comprehensive Income (Detail)</link:definition>
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        <link:usedOn>link:presentationLink</link:usedOn>
        <link:usedOn>link:definitionLink</link:usedOn>
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        <link:definition>1124 - Disclosure - Related Parties - Additional Information (Detail)</link:definition>
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  <element name="DefinedBenefitPlanContributionsByPlanParticipantsToPlanAssets" id="iclr_DefinedBenefitPlanContributionsByPlanParticipantsToPlanAssets" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="DefinedBenefitPlanExpectedLongTermReturnOnAssetsAfterApplicationOfMarketValueReductionFactor" id="iclr_DefinedBenefitPlanExpectedLongTermReturnOnAssetsAfterApplicationOfMarketValueReductionFactor" type="num:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="DefinedBenefitPlanHighQualityBondMaturityMaximumRangeUsedToDetermineYieldCurvePeriod" id="iclr_DefinedBenefitPlanHighQualityBondMaturityMaximumRangeUsedToDetermineYieldCurvePeriod" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="DocumentAndEntityInformationAbstract" id="iclr_DocumentAndEntityInformationAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="EmployeeMember" id="iclr_EmployeeMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="EmployeeStockPlanTwentyZeroEightPlanMember" id="iclr_EmployeeStockPlanTwentyZeroEightPlanMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="EmployeeStockPlanTwentyZeroThreePlanMember" id="iclr_EmployeeStockPlanTwentyZeroThreePlanMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="ExpectedRetirementPeriod" id="iclr_ExpectedRetirementPeriod" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="FiniteLivedIntangibleAssetsAccumulatedAmortizationsForeignExchangeMovement" id="iclr_FiniteLivedIntangibleAssetsAccumulatedAmortizationsForeignExchangeMovement" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="FiniteLivedIntangibleAssetsAmortizationExpenseNet" id="iclr_FiniteLivedIntangibleAssetsAmortizationExpenseNet" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="FirecrestClinicalMember" id="iclr_FirecrestClinicalMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ForeignCurrencyDisclosureTableTextBlock" id="iclr_ForeignCurrencyDisclosureTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="FourZeroOneKPlanMember" id="iclr_FourZeroOneKPlanMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="GovernmentGrantsDisclosureTextBlock" id="iclr_GovernmentGrantsDisclosureTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="GovernmentGrantsPolicyTextBlock" id="iclr_GovernmentGrantsPolicyTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="GovernmentGrantsTable" id="iclr_GovernmentGrantsTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="GovernmentGrantsTableTextBlock" id="iclr_GovernmentGrantsTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="HealthcareDiscoveriesIncMember" id="iclr_HealthcareDiscoveriesIncMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="IboxxCorporateBondsMember" id="iclr_IboxxCorporateBondsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="IncomeBeforeIncomeTaxTableTextBlock" id="iclr_IncomeBeforeIncomeTaxTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="IncomeTaxBenefitMember" id="iclr_IncomeTaxBenefitMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="InterestOnShortTermInvestments" id="iclr_InterestOnShortTermInvestments" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="LegalAndGeneralActiveCorporateBondOverTenYearMember" id="iclr_LegalAndGeneralActiveCorporateBondOverTenYearMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="LegalAndGeneralGiltFundsMember" id="iclr_LegalAndGeneralGiltFundsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="LegalAndGeneralIndexLinkedGiltFundsMember" id="iclr_LegalAndGeneralIndexLinkedGiltFundsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="LegalAndGeneralOver15YearGiltsIndexMember" id="iclr_LegalAndGeneralOver15YearGiltsIndexMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="MediaPharmaSolutionsMember" id="iclr_MediaPharmaSolutionsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="MediMediaPharmaSolutionsMember" id="iclr_MediMediaPharmaSolutionsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="NewAndRecentAccountingPronouncementsDisclosureTextBlock" id="iclr_NewAndRecentAccountingPronouncementsDisclosureTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="NumberOfClinicalResearchSitesAcquired" id="iclr_NumberOfClinicalResearchSitesAcquired" type="xbrli:integerItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="NumberOfLocations" id="iclr_NumberOfLocations" type="xbrli:integerItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="NumberOfPatients" id="iclr_NumberOfPatients" type="xbrli:integerItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OnerousLeaseMember" id="iclr_OnerousLeaseMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OpenTaxYears" id="iclr_OpenTaxYears" type="us-types:durationStringItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OperatingIncomeByGeographyTableTextBlock" id="iclr_OperatingIncomeByGeographyTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OperatingIncomeLossBeforeRestructuringCharges" id="iclr_OperatingIncomeLossBeforeRestructuringCharges" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="OperatingLossCarryforwardsUSFederal" id="iclr_OperatingLossCarryforwardsUSFederal" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="OtherComprehensiveIncomeAmortizationOfNetPeriodServiceCreditNetOfTax" id="iclr_OtherComprehensiveIncomeAmortizationOfNetPeriodServiceCreditNetOfTax" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentBeforeTaxLongTermFunding" id="iclr_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentBeforeTaxLongTermFunding" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentLongTermFundingTax" id="iclr_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentLongTermFundingTax" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OtherCountriesMember" id="iclr_OtherCountriesMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OtherLiabilitiesLineItems" id="iclr_OtherLiabilitiesLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OtherLiabilitiesTable" id="iclr_OtherLiabilitiesTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="OtherPlanAssetCategoriesMember" id="iclr_OtherPlanAssetCategoriesMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="OxfordOutcomesLimitedMember" id="iclr_OxfordOutcomesLimitedMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PaymentsForShareRepurchaseCosts" id="iclr_PaymentsForShareRepurchaseCosts" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PerformanceBasedGrantsMember" id="iclr_PerformanceBasedGrantsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PerformanceShareUnitMember" id="iclr_PerformanceShareUnitMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PeriodFiveMember" id="iclr_PeriodFiveMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PeriodFourMember" id="iclr_PeriodFourMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="PeriodSixMember" id="iclr_PeriodSixMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PeriodThreeMember" id="iclr_PeriodThreeMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PeriodTwoMember" id="iclr_PeriodTwoMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PmgResearchIncorporatedMember" id="iclr_PmgResearchIncorporatedMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PrevalereLifeSciencesMember" id="iclr_PrevalereLifeSciencesMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="PriceSpectiveLlcMember" id="iclr_PriceSpectiveLlcMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range10Member" id="iclr_Range10Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range11Member" id="iclr_Range11Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range12Member" id="iclr_Range12Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range13Member" id="iclr_Range13Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range14Member" id="iclr_Range14Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range15Member" id="iclr_Range15Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range16Member" id="iclr_Range16Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range17Member" id="iclr_Range17Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range18Member" id="iclr_Range18Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range19Member" id="iclr_Range19Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range1Member" id="iclr_Range1Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range20Member" id="iclr_Range20Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range21Member" id="iclr_Range21Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range22Member" id="iclr_Range22Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range23Member" id="iclr_Range23Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="Range24Member" id="iclr_Range24Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="Range9Member" id="iclr_Range9Member" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="ReconciliationOfProvisionOfIncomeTaxesTable" id="iclr_ReconciliationOfProvisionOfIncomeTaxesTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="RecoveryOfAmortizationOfGovernmentGrants" id="iclr_RecoveryOfAmortizationOfGovernmentGrants" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="credit" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="RelatedPartyOneMember" id="iclr_RelatedPartyOneMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="RestOfEuropeMember" id="iclr_RestOfEuropeMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="RestOfWorldMember" id="iclr_RestOfWorldMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="RestrictedStockUnitsTwentyThirteenMember" id="iclr_RestrictedStockUnitsTwentyThirteenMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="RestrictedStockUnitsTwentyZeroEightMember" id="iclr_RestrictedStockUnitsTwentyZeroEightMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="RestructuringChargesTableTextBlock" id="iclr_RestructuringChargesTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="RestructuringProgramAxis" id="iclr_RestructuringProgramAxis" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:dimensionItem"/>
  <element name="RestructuringProgramDomain" id="iclr_RestructuringProgramDomain" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="RestructuringReserveAccrualAdjustmentRelatedToAssetWriteoff" id="iclr_RestructuringReserveAccrualAdjustmentRelatedToAssetWriteoff" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="RestructuringReserveUtilizations" id="iclr_RestructuringReserveUtilizations" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="duration" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item"/>
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  <element name="ScheduleOfAccruedLiabilitiesTable" id="iclr_ScheduleOfAccruedLiabilitiesTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="ScheduleOfAssumptionsUsedInCalculatingNetPeriodicBenefitCostTableTextBlock" id="iclr_ScheduleOfAssumptionsUsedInCalculatingNetPeriodicBenefitCostTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfCapitalExpendituresByGeographicAreaTableTextBlock" id="iclr_ScheduleOfCapitalExpendituresByGeographicAreaTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfCashFlowSupplementalLineItems" id="iclr_ScheduleOfCashFlowSupplementalLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfCashFlowSupplementalTable" id="iclr_ScheduleOfCashFlowSupplementalTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="ScheduleOfComponentsOfIncomeBeforeIncomeTaxExpenseBenefitLineItems" id="iclr_ScheduleOfComponentsOfIncomeBeforeIncomeTaxExpenseBenefitLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfComponentsOfIncomeBeforeIncomeTaxExpenseBenefitTable" id="iclr_ScheduleOfComponentsOfIncomeBeforeIncomeTaxExpenseBenefitTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="ScheduleOfDeferredIncomeTaxAssetsAndLiabilitiesLineItems" id="iclr_ScheduleOfDeferredIncomeTaxAssetsAndLiabilitiesLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfDeferredIncomeTaxAssetsAndLiabilitiesTable" id="iclr_ScheduleOfDeferredIncomeTaxAssetsAndLiabilitiesTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="ScheduleOfDepreciationAndAmortizationExpenseByGeographicalAreaTableTextBlock" id="iclr_ScheduleOfDepreciationAndAmortizationExpenseByGeographicalAreaTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfIncomeTaxExpenseBenefitByGeographicAreaTableTextBlock" id="iclr_ScheduleOfIncomeTaxExpenseBenefitByGeographicAreaTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfInterestIncomBySegmentTableTextBlock" id="iclr_ScheduleOfInterestIncomBySegmentTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfNonCashStockCompensationExpenseTableTextBlock" id="iclr_ScheduleOfNonCashStockCompensationExpenseTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfShareBasedCompensationRestrictedStockUnitsPerformanceStockUnitsAwardActivityTableTextBlock" id="iclr_ScheduleOfShareBasedCompensationRestrictedStockUnitsPerformanceStockUnitsAwardActivityTableTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfUsefulLivesForPropertyPlantEquipmentTextBlock" id="iclr_ScheduleOfUsefulLivesForPropertyPlantEquipmentTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfWeightedAverageNumberOfDilutedSharesOutstandingLineItems" id="iclr_ScheduleOfWeightedAverageNumberOfDilutedSharesOutstandingLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ScheduleOfWeightedAverageNumberOfDilutedSharesOutstandingTable" id="iclr_ScheduleOfWeightedAverageNumberOfDilutedSharesOutstandingTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonvestedOptionsForfeitedInPeriodWeightedAverageExercisePrice" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonvestedOptionsForfeitedInPeriodWeightedAverageExercisePrice" type="num:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonvestedOptionsGrantedInPeriodWeightedAverageExercisePrice" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonvestedOptionsGrantedInPeriodWeightedAverageExercisePrice" type="num:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonvestedOptionsOutstandingExercisePriceAbstract" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonvestedOptionsOutstandingExercisePriceAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonvestedOptionsOutstandingWeightedAverageExercisePrice" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonvestedOptionsOutstandingWeightedAverageExercisePrice" type="num:perShareItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNonvestedOptionsVestedInPeriodWeightedAverageExercisePrice" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonvestedOptionsVestedInPeriodWeightedAverageExercisePrice" type="num:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForAdditionalGrant" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForAdditionalGrant" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrant" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrant" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantAbstract" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantGrantsInPeriod" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantGrantsInPeriod" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantOptionsCancelledInPeriod" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantOptionsCancelledInPeriod" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantOptionsExercisedInPeriod" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAvailableForGrantOptionsExercisedInPeriod" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableAndVestedWeightedAverageGrantDateFairValue" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableAndVestedWeightedAverageGrantDateFairValue" type="num:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodWeightedAverageGrantDateFairValue" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodWeightedAverageGrantDateFairValue" type="num:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpectedToVestOutstandingNumber" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpectedToVestOutstandingNumber" type="xbrli:sharesItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageGrantDateFairValue" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageGrantDateFairValue" type="num:perShareItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageGrantDateFairValue" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageGrantDateFairValue" type="num:perShareItemType" abstract="false" xbrli:periodType="instant" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsWeightedAverageGrantDateFairValueAbstract" id="iclr_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsWeightedAverageGrantDateFairValueAbstract" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherThanOptionsExpectedVestingPeriod" id="iclr_ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherThanOptionsExpectedVestingPeriod" type="xbrli:gYearItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShortTermAvailableForSaleInvestmentsAverageRemainingMaturityPeriod" id="iclr_ShortTermAvailableForSaleInvestmentsAverageRemainingMaturityPeriod" type="xbrli:durationItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="ShortTermInvestmentsPolicyTextBlock" id="iclr_ShortTermInvestmentsPolicyTextBlock" type="nonnum:textBlockItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="SignificantAccountingPoliciesLineItems" id="iclr_SignificantAccountingPoliciesLineItems" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="SignificantAccountingPoliciesTable" id="iclr_SignificantAccountingPoliciesTable" type="xbrli:stringItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrldt:hypercubeItem"/>
  <element name="StockOptionAndAwardPlansMember" id="iclr_StockOptionAndAwardPlansMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="StockRepurchaseProgramAuthorizedPercentage" id="iclr_StockRepurchaseProgramAuthorizedPercentage" type="num:percentItemType" abstract="false" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="TechnologyAssetsMember" id="iclr_TechnologyAssetsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="TermDepositsMember" id="iclr_TermDepositsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="TwoThousandAndSixteenMember" id="iclr_TwoThousandAndSixteenMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="UnitedKingdomTreasuryBondSecuritiesMember" id="iclr_UnitedKingdomTreasuryBondSecuritiesMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="VehiclesGross" id="iclr_VehiclesGross" type="xbrli:monetaryItemType" abstract="false" xbrli:periodType="instant" xbrli:balance="debit" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="VestedAndNonVestedOptionsMember" id="iclr_VestedAndNonVestedOptionsMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="VolunteerListMember" id="iclr_VolunteerListMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
  <element name="WorkforceReductionMember" id="iclr_WorkforceReductionMember" type="nonnum:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" substitutionGroup="xbrli:item"/>
</schema>





