<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2023-03-31</periodOfReport>

    <noSecuritiesOwned>1</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001095651</issuerCik>
        <issuerName>ISTAR INC.</issuerName>
        <issuerTradingSymbol>SAFE</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000936828</rptOwnerCik>
            <rptOwnerName>GIC Private Ltd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>168 ROBINSON ROAD</rptOwnerStreet1>
            <rptOwnerStreet2>#37-01 CAPITAL TOWER</rptOwnerStreet2>
            <rptOwnerCity>SINGAPORE</rptOwnerCity>
            <rptOwnerState>U0</rptOwnerState>
            <rptOwnerZipCode>068912</rptOwnerZipCode>
            <rptOwnerStateDescription>SINGAPORE</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001709755</rptOwnerCik>
            <rptOwnerName>GIC Real Estate Private Ltd</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GIC PRIVATE LIMITED</rptOwnerStreet1>
            <rptOwnerStreet2>168 ROBINSON ROAD, #37-01 CAPITAL TOWER</rptOwnerStreet2>
            <rptOwnerCity>SINGAPORE</rptOwnerCity>
            <rptOwnerState>U0</rptOwnerState>
            <rptOwnerZipCode>068912</rptOwnerZipCode>
            <rptOwnerStateDescription>SINGAPORE</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001709752</rptOwnerCik>
            <rptOwnerName>GIC Real Estate, Inc.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>ONE BUSH STREET, SUITE 1000</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94104</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001709649</rptOwnerCik>
            <rptOwnerName>SFTY Venture LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O GIC REAL ESTATE, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>280 PARK AVENUE, 9TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10017</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <footnotes></footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>GIC PRIVATE LIMITED, By: /s/ Glien Tan Cheng Chuan, Name: Glien Tan Cheng Chuan, Title: Managing Director; By: /s/ Toh Tze Meng, Name: Toh Tze Meng, Title: Senior Vice President</signatureName>
        <signatureDate>2023-04-04</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>GIC REAL ESTATE PRIVATE LIMITED, By: /s/ Chan Hoe Yin, Name: Chan Hoe Yin, Title: Director</signatureName>
        <signatureDate>2023-04-04</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>GIC REAL ESTATE, INC., By: /s/ Kristin Leung, Name: Kristin Leung, Title: Managing Director</signatureName>
        <signatureDate>2023-04-04</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>SFTY VENTURE LLC, By: /s/ Kristin Leung, Name: Kristin Leung, Title: Managing Director</signatureName>
        <signatureDate>2023-04-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
