<SEC-DOCUMENT>0000049826-18-000071.txt : 20180508
<SEC-HEADER>0000049826-18-000071.hdr.sgml : 20180508
<ACCEPTANCE-DATETIME>20180508162902
ACCESSION NUMBER:		0000049826-18-000071
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20180504
FILED AS OF DATE:		20180508
DATE AS OF CHANGE:		20180508

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Williams Anre D
		CENTRAL INDEX KEY:			0001303170

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-04797
		FILM NUMBER:		18815045

	MAIL ADDRESS:	
		STREET 1:		ILLINOIS TOOL WORKS INC.
		STREET 2:		155 HARLEM AVE.
		CITY:			GLENVIEW
		STATE:			IL
		ZIP:			60025

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			ILLINOIS TOOL WORKS INC
		CENTRAL INDEX KEY:			0000049826
		STANDARD INDUSTRIAL CLASSIFICATION:	GENERAL INDUSTRIAL MACHINERY & EQUIPMENT [3560]
		IRS NUMBER:				361258310
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		155 HARLEM AVENUE
		CITY:			GLENVIEW
		STATE:			IL
		ZIP:			60025
		BUSINESS PHONE:		8477247500

	MAIL ADDRESS:	
		STREET 1:		155 HARLEM AVENUE
		CITY:			GLENVIEW
		STATE:			IL
		ZIP:			60025
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_152581128772621.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-05-04</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000049826</issuerCik>
        <issuerName>ILLINOIS TOOL WORKS INC</issuerName>
        <issuerTradingSymbol>ITW</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001303170</rptOwnerCik>
            <rptOwnerName>Williams Anre D</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>AMERICAN EXPRESS COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>200 VESEY STREET, 40TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10285</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2018-05-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>996</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>145.47</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>21741</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Phantom Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1195.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1195</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents shares of common stock acquired pursuant to the Illinois Tool Works Inc. 2015 Long-Term Incentive Plan representing an annual stock grant.</footnote>
        <footnote id="F2">Represents units of phantom stock under the Phantom Stock Plan for non-employee directors as of May 4, 2018.  Each unit is equal in value to one share of common stock.  The units are not transferable and have no voting rights.  Additional units are credited in amounts equivalent to cash dividends paid on the common stock.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Anre D. Williams by Janet O. Love, Deputy General Counsel &amp; Assistant Secretary, Attorney-in-Fact POA on File</signatureName>
        <signatureDate>2018-05-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
