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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-03-08</periodOfReport>

    <issuer>
        <issuerCik>0000097216</issuerCik>
        <issuerName>TEREX CORP</issuerName>
        <issuerTradingSymbol>TEX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001656422</rptOwnerCik>
            <rptOwnerName>GARRISON JOHN L JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TEREX CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>200 NYALA FARM ROAD</rptOwnerStreet2>
            <rptOwnerCity>WESTPORT</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06880</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>CEO AND PRESIDENT</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2018-03-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>58363</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>692787</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2018-03-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>54194</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>746981</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2018-03-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>54194</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>801175</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Shares granted pursuant to one of the Company's long-term incentive plans with the award vesting as follows: 1/3 on March 8, 2019; 1/3 on March 8, 2020 and 1/3 on March 8, 2021.</footnote>
        <footnote id="F2">Shares granted pursuant to one of the Company's long-term incentive plans with the award scheduled to vest in the first quarter of 2021 if the Company achieves a targeted percentile rank against a peer group of companies for three year annualized total shareholder return (&quot;TSR&quot;) for the period January 1, 2018 - December 31, 2020.  The number of shares in this grant are subject to adjustment, up or down, based upon attainment above or below the targeted percentile rank.</footnote>
        <footnote id="F3">Shares granted pursuant to one of the Company's long-term incentive plans with the award scheduled to vest in the first quarter of 2021 if the Company achieves a targeted return on invested capital (&quot;ROIC&quot;) in each of 2018, 2019 and 2020.  The number of shares in this grant are subject to adjustment, up or down, based upon attainment above or below the targeted ROIC.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/Scott J. Posner, by power of attorney</signatureName>
        <signatureDate>2018-03-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2018-03-08
0000097216
TEREX CORP
TEX
0001656422
GARRISON JOHN L JR
C/O TEREX CORPORATION
200 NYALA FARM ROAD
WESTPORT
CT
06880
1
1
0
0
CEO AND PRESIDENT
Common Stock, par value $.01
2018-03-08
4
A
0
58363
0
A
692787
D
Common Stock, par value $.01
2018-03-08
4
A
0
54194
0
A
746981
D
Common Stock, par value $.01
2018-03-08
4
A
0
54194
0
A
801175
D
Shares granted pursuant to one of the Company's long-term incentive plans with the award vesting as follows: 1/3 on March 8, 2019; 1/3 on March 8, 2020 and 1/3 on March 8, 2021.
Shares granted pursuant to one of the Company's long-term incentive plans with the award scheduled to vest in the first quarter of 2021 if the Company achieves a targeted percentile rank against a peer group of companies for three year annualized total shareholder return ("TSR") for the period January 1, 2018 - December 31, 2020.  The number of shares in this grant are subject to adjustment, up or down, based upon attainment above or below the targeted percentile rank.
Shares granted pursuant to one of the Company's long-term incentive plans with the award scheduled to vest in the first quarter of 2021 if the Company achieves a targeted return on invested capital ("ROIC") in each of 2018, 2019 and 2020.  The number of shares in this grant are subject to adjustment, up or down, based upon attainment above or below the targeted ROIC.
/s/Scott J. Posner, by power of attorney
2018-03-12