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    <submissionType>144</submissionType>
    <filerInfo>
      <filer>
        <filerCredentials>
          <cik>0001861730</cik>
          <ccc>XXXXXXXX</ccc>
        </filerCredentials>
      </filer>
      <liveTestFlag>LIVE</liveTestFlag>



    </filerInfo>
  </headerData>
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    <issuerInfo>
      <issuerCik>0001842718</issuerCik>
      <issuerName>INTEGRAL AD SCIENCE HOLDING CORP.</issuerName>
      <secFileNumber>001-40557</secFileNumber>
      <issuerAddress>
        <com:street1>99 WALL STREET</com:street1>
        <com:street2>#1950</com:street2>
        <com:city>NEW YORK</com:city>
        <com:stateOrCountry>NY</com:stateOrCountry>
        <com:zipCode>10005</com:zipCode>
      </issuerAddress>
      <issuerContactPhone>(646) 278-4871</issuerContactPhone>
      <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>SHARMA TOM</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
      <relationshipsToIssuer>
        <relationshipToIssuer>Officer</relationshipToIssuer>
      </relationshipsToIssuer>
    </issuerInfo>
    <securitiesInformation>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <brokerOrMarketmakerDetails>
        <name>Fidelity Brokerage Services LLC</name>
        <address>
          <com:street1>900 Salem Street</com:street1>
          <com:city>Smithfield</com:city>
          <com:stateOrCountry>RI</com:stateOrCountry>
          <com:zipCode>02917</com:zipCode>
        </address>
      </brokerOrMarketmakerDetails>
      <noOfUnitsSold>28385</noOfUnitsSold>
      <aggregateMarketValue>397919.87</aggregateMarketValue>
      <noOfUnitsOutstanding>154417454</noOfUnitsOutstanding>
      <approxSaleDate>03/22/2023</approxSaleDate>
      <securitiesExchangeName>NASDAQ</securitiesExchangeName>
    </securitiesInformation>
    <securitiesToBeSold>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <acquiredDate>03/22/2023</acquiredDate>
      <natureOfAcquisitionTransaction>Option Granted - 11/02/2020</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>28385</amountOfSecuritiesAcquired>
      <paymentDate>03/22/2023</paymentDate>
      <natureOfPayment>Cash</natureOfPayment>
    </securitiesToBeSold>
    <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>Kshitij Sharma</name>
        <address>
          <com:street1>99 Wall Street</com:street1>
          <com:street2>#1950</com:street2>
          <com:city>New York</com:city>
          <com:stateOrCountry>NY</com:stateOrCountry>
          <com:zipCode>10005</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>Common</securitiesClassTitle>
      <saleDate>03/21/2023</saleDate>
      <amountOfSecuritiesSold>4200</amountOfSecuritiesSold>
      <grossProceeds>58802.10</grossProceeds>
    </securitiesSoldInPast3Months>
    <remarks>Tom Sharma and Kshitij Sharma are one and the same person.</remarks>
    <noticeSignature>
      <noticeDate>03/22/2023</noticeDate>
      <planAdoptionDates>
        <planAdoptionDate>12/15/2022</planAdoptionDate>
      </planAdoptionDates>
      <signature>/s/ Jennifer Ruchti, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Kshitij Sharma</signature>
    </noticeSignature>
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144
0001861730
XXXXXXXX
LIVE
0001842718
INTEGRAL AD SCIENCE HOLDING CORP.
001-40557
99 WALL STREET
#1950
NEW YORK
NY
10005
(646) 278-4871
SHARMA TOM
Officer
Common
Fidelity Brokerage Services LLC
900 Salem Street
Smithfield
RI
02917
28385
397919.87
154417454
03/22/2023
NASDAQ
Common
03/22/2023
Option Granted - 11/02/2020
Issuer
N
28385
03/22/2023
Cash
N
Kshitij Sharma
99 Wall Street
#1950
New York
NY
10005
Common
03/21/2023
4200
58802.10
Tom Sharma and Kshitij Sharma are one and the same person.
03/22/2023
12/15/2022
/s/ Jennifer Ruchti, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Kshitij Sharma