EXECUTION VERSION TAX SHARING AGREEMENT between MORGAN STANLEY, on behalf of itself and the members of the MS Group, and MSCI INC., on behalf of itself and the members of the MSCI Group

Exhibit 10.12

EXECUTION VERSION

TAX SHARING AGREEMENT

between

MORGAN STANLEY,

on behalf of itself

and the members

of the MS Group,

and

MSCI INC.,

on behalf of itself

and the members

of the MSCI Group

This Agreement is entered into as of the 20 ^th day of November, 2007 between Morgan Stanley (“ MS ”), a Delaware corporation, on behalf of itself and the members of the MS Group, as defined below, and MSCI Inc. (“ MSCI ”), a Delaware corporation, registered to do business in New York as NY MSCI, on behalf of itself and the members of the MSCI Group, as defined below.

WITNESSETH:

WHEREAS, pursuant to the tax laws of various jurisdictions, certain members of the MSCI Group presently file, and will continue to file prior to certain transactions, certain tax returns on an affiliated, consolidated, combined, unitary, fiscal unity or other group basis (including as permitted by Section 1501 of the Internal Revenue Code of 1986, as amended (the “ Code ”)) with certain members of the MS Group;

NOW, THEREFORE, in consideration of the mutual covenants and agreements hereinafter set forth, the parties agree as follows:

1. Definitions.

(a) As used in this Agreement:

“ Actually Realized ” or “Actually Realizes ” shall mean, for purposes of determining the timing of the incurrence of any Tax liability or the realization of a Refund (or any related income tax or other Tax cost or benefit) in respect of any payment, transaction, occurrence or event, the time at which the amount of income taxes paid (or Refund realized) is increased above (or reduced below) the amount of income taxes that would otherwise have been required to be paid (or Refund that would otherwise have been realized) but for such payment, transaction, occurrence or event.

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“ Affiliate ” of any Person shall mean any individual, corporation, partnership or other entity directly or indirectly owning more than 50 percent (by vote or value) of, owned more than 50 percent (by vote or value) by, or under more than 50 percent (by vote or value) common ownership with, such Person.

“ After-Tax Amount ” shall mean an additional amount necessary to reflect the hypothetical Tax consequences of the receipt or accrual of any payment, using the maximum statutory rate (or rates, in the case of an item that affects more than one Tax) applicable to the recipient of such payment for the relevant Taxable year, reflecting for example, the effect of the deductions available for interest paid or accrued and for Taxes, such as state and local income taxes.

“ AMT ” shall mean the alternative minimum tax, within the meaning of Section 55 of the Code.

“ Barra ” shall mean Barra, Inc., a Delaware corporation.

“ Code ” shall have the meaning ascribed to it in the first “whereas” clause in this Agreement.

“ Combined Apportionment Factor ” shall mean the apportionment factor reflected on the applicable consolidated, combined or unitary state or local income tax return and utilized in computing the combined, consolidated or unitary state or local income tax liability.

“ Consolidated Federal Return ” shall mean a Pre-Deconsolidation Period Return filed in respect of federal income taxes by a Consolidated Group.

“ Consolidated Group ” shall mean any group consisting of (i) at least one member of the MS Group that filed (or will file) any Pre-Deconsolidation Period Return that reflects the income, assets or operations of any member of the MSCI Group or (ii) at least one member of the MSCI Group that filed (or will file) any Pre-Deconsolidation Period Return that reflects the income, assets or operations of any member of the MS Group.

“ Consolidated State Return ” shall mean a Pre-Deconsolidation Period Return filed in respect of state or local income taxes by a Consolidated Group.

“ Deconsolidation Date ” shall mean with respect to a Return the date on which any member of the MSCI Group is no longer consolidated, combined or in a unitary relationship (as the case may be) with any member of MS Group in filing such Return.

“ Federal Separate Group Tax Liability ” shall mean the product of a Group’s Separate Group Taxable Income, computed for federal income tax

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purposes, and the highest federal income tax rate imposed under the Code on the Taxable income of a corporation for the relevant Taxable period (or portion thereof), reduced by any Tax credits that the Group would be able to use if it were calculating its federal income Tax liability on a stand-alone basis.

“ Final Determination ” shall mean (i) with respect to federal income taxes, (A) a “determination” as defined in Section 1313(a) of the Code, or (B) the date of acceptance by or on behalf of the IRS of Form 870-AD (or any successor form thereto), as a final resolution of Tax liability for any Taxable period, except that a Form 870-AD (or successor form thereto) that reserves the right of the taxpayer to file a claim for Refund or the right of the IRS to assert a further deficiency shall not constitute a Final Determination with respect to the item or items so reserved; (ii) with respect to Taxes other than federal income taxes, any final determination of liability in respect of a Tax that, under applicable law, is not subject to further appeal, review or modification through proceedings or otherwise; (iii) with respect to any Tax, any final disposition by reason of the expiration of the applicable statute of limitations; or (iv) with respect to any Tax, the payment of Tax by any member of the MS Group or the MSCI Group, whichever is responsible for payment of such Tax under applicable law, with respect to any item disallowed or adjusted by a Taxing Authority, provided that the provisions of Section 13 hereof have been complied with, or, if such section is inapplicable, that the party responsible under the terms of this Agreement for such Tax is notified by the party paying such Tax that it has determined that no action should be taken to recoup such disallowed item, and the other party agrees with such determination.

“ Gain Group ” shall mean a Group with Separate Group Taxable Income for the relevant Taxable period.

“ Group ” shall mean the MSCI Group or the MS Group, as appropriate. “ IRS ” shall mean the Internal Revenue Service.

“ Loss Group ” shall mean a Group that incurs a Separate Group Taxable Loss for the relevant Taxable period.

“ MSCI Group ” shall mean one or more of (i) MSCI, (ii) on or before the Deconsolidation Date, any Person that is, or was, a Subsidiary of MSCI for such period of ownership by MSCI and (iii) to the extent not previously included by (ii), Barra and its Subsidiaries, including for (i), (ii) and (iii) any predecessors and successors thereto.

“ MS Group ” shall mean one or more of MS and its Subsidiaries other than those entities comprising the MSCI Group.

“ Overpayment Rate ” shall mean the overpayment rate as set forth in Section 6621 of the Code.

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“ Person ” shall have the meaning ascribed to it in Section 7701(a)(1) of the Code.

“ Post-Deconsolidation Period ” shall mean any Taxable period (or portion thereof) beginning after the close of business on the Deconsolidation Date.

“ Pre-Deconsolidation Period ” shall mean any Taxable period ending on or before the close of business on the Deconsolidation Date; provided that if a Taxable period ending after the Deconsolidation Date contains any days which fall prior to or on the Deconsolidation Date, only the portion of such Taxable period up to and including the Deconsolidation Date shall be included in the Pre-Deconsolidation Period.

“ Refund ” shall mean any refund of Taxes, including any reduction in Taxes by means of a credit, offset or otherwise.

“ Return ” shall mean any Tax return, statement, report, form, election, claim or surrender (including estimated Tax returns and reports, extension requests and forms, and information returns and reports) required to be filed with any Taxing Authority.

“ Separate Group Taxable Income ” shall mean, with respect to a Group, such Group’s Taxable income computed as if such Group were a separate consolidated, combined or unitary group, and applying such Tax principles, including limitations and carryovers (excluding limits for charitable contributions and dividends-received deduction, and accounting for deferred intercompany transactions consistent with the deferral and recognition rules of Treasury Regulations Section 1.1502-13 (or any successor rule) or analogous state or local rule), that would have been applicable to such Group had such Group never been part of the Consolidated Group or any other consolidated, combined or unitary group. In the context of state and local tax, Separate Group Taxable Income shall be computed prior to the application of any apportionment formula. Additionally, to the extent a member of a Group has a net operating loss or any other tax attribute that was created prior to becoming a member of the Group but can be carried forward and used by the Group (in the context of state or local law, either before or after apportionment, as determined under applicable law), such attribute will factor into such Group’s calculation of Separate Group Taxable Income (taking into account any applicable limitations on the use thereof).

“ Separate Group Taxable Loss ” shall mean, with respect to a Group, such Group’s Taxable loss computed as if such Group were a separate consolidated, combined or unitary group, and applying such Tax principles, including limitations and carryovers (excluding limits for charitable contributions and dividends-received deduction, and accounting for deferred intercompany transactions consistent with the deferral and recognition rules of Treasury Regulations Section 1.1502-13 (or any successor rule) or analogous state or local rule), that would have been applicable to such Group had such Group never been

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part of the Consolidated Group or any other consolidated, combined or unitary group. In the context of state and local tax, Separate Group Taxable Loss shall be computed prior to the application of any apportionment formula. Additionally, to the extent a member of a Group has a net operating loss or any other Tax attribute that was created prior to becoming a member of the Group but can be carried forward and used by the Group (in the context of state or local law, either before or after apportionment, as determined under applicable law), such attribute will factor into the Group’s calculation of Separate Group Taxable Loss (taking into account any applicable limitations on the use thereof).

“ State Separate Group Tax Liability ” shall mean, with respect to a particular state or locality, the product of the Group’s Separate Group Taxable Income and the Combined Apportionment Factor and the State Tax Rate, reduced by any applicable Tax credits that the Group would be able to use if it were calculating its Tax liability on a stand-alone basis.

“ State Tax Rate ” shall mean, with respect to a particular state or locality, the highest applicable tax rate imposed under applicable law on the Separate Group Taxable Income of the Group for the relevant Taxable period (or portion thereof).

“ Subsidiary ” of any Person shall mean any corporation, partnership or other entity directly or indirectly owned more than 50 percent (by vote or value) by such Person.

“ Tax ” (and the correlative meaning, “ Taxes ,” “ Taxing ” and “ Taxable ”) shall mean (A) any tax imposed under Subtitle A of the Code, or any net income, gross income, gross receipts, alternative or add-on minimum, sales, use, business and occupation, value-added, trade, goods and services, ad valorem, franchise, profits, license, business royalty, withholding, payroll, employment, capital, excise, transfer, recording, severance, stamp, occupation, premium, property, asset, real estate acquisition, environmental, custom duty, or other tax, governmental fee or other like assessment or charge of any kind whatsoever, together with any interest and any penalty, addition to tax or additional amount imposed by a Taxing Authority; (B) any liability of a member of the MS Group or the MSCI Group, as the case may be, for the payment of any amounts of the type described in clause (A) for any Taxable period resulting from such member being a part of a consolidated group pursuant to the application of Treasury Regulations Section 1.1502-6 or any similar provision applicable under state, local or foreign law; or (C) any liability of a member of the MS Group or the MSCI Group for the payment of any amounts described in clause (A) as a result of any express or implied obligation to indemnify any other Person.

“ Tax Benefit ” shall have the meaning ascribed to it in Section 10(d) of this Agreement.

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“ Tax Proceeding ” shall mean any Tax audit, dispute or proceeding (whether administrative, judicial or contractual).

“ Taxing Authority ” shall mean any governmental authority (domestic or foreign), including, without limitation, any state, municipality, political subdivision or governmental agency, responsible for the imposition of any Tax.

“ Underpayment Rate ” shall mean the underpayment rate as set forth in Section 6621 of the Code.

(b) Any term used in this Agreement which is not defined in this Agreement shall, to the extent the context requires, have the meaning assigned to it in the Code or the applicable Treasury regulations thereunder (as interpreted in administrative pronouncements and judicial decisions), or in comparable provisions of applicable law.

2. Tax Sharing Agreements. Any and all existing Tax sharing agreements or arrangements, written or unwritten, between any member of the MS Group and any member of the MSCI Group, other than this Agreement, shall terminate upon the execution of this Agreement. Upon the execution of this Agreement, neither the members of the MSCI Group nor the members of the MS Group shall have any further rights or liabilities thereunder, and this Agreement shall be the only Tax sharing agreement between the members of the MSCI Group and the members of the MS Group. MS and MSCI shall act in good faith in the performance of this Agreement.

3. Federal Income Taxes.

(a) Return Filing.

(i) MS shall prepare and file, or cause to be prepared and filed, Consolidated Federal Returns for which the Consolidated Group is required or permitted to file a Consolidated Federal Return using, inter alia, information provided by MSCI. MSCI shall provide MS with all necessary information to file a Consolidated Federal Return not later than 45 days after MS’s fiscal year-end and shall respond promptly to all information requests, but in no event more than two business days following a request. Each member of the Consolidated Group shall execute and file such consents, elections and other documents as may be required or appropriate for the filing of such Consolidated Federal Returns. All Tax elections shall be at the sole discretion of MS provided, however, that MSCI shall be entitled to direct MS to make any and all Tax elections that exclusively affect the MSCI Group, subject to MS’s consent. All income tax computations performed on a consolidated basis will be performed or approved by MS. MS shall not change any method of accounting that

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relates exclusively to the MSCI Group for any Tax purpose if such change adversely affects the MSCI Group unless such change is required by law. MS shall notify and discuss with MSCI prior to the filing of a Consolidated Federal Return any potential material differences in the information provided by MSCI to be used in the preparation of such Consolidated Federal Return and the position MS intends to take on such Consolidated Federal Return.

(ii) MS shall pay, or cause to be paid, and, subject to the provisions of Section 3(b), shall be responsible for, any and all federal income taxes due or required to be paid with respect to, or required to be reported on, any such Consolidated Federal Return.

(iii) In the event a Consolidated Federal Return is not filed, each relevant member of the MS Group and MSCI Group shall be responsible for (i) filing its own Pre-Deconsolidation Period Return in respect of federal income taxes as a separate entity, including requests for extension, as if this Agreement were not in effect and (ii) making Tax payments (including estimated Tax payments, if necessary). Each such member filing a Return as a separate entity shall be entitled to any Tax Benefit and shall be liable for any Tax burden resulting from the filing of such separate Return.

(b) Allocated Tax Charge.

(i) MS shall be responsible for calculating the Separate Group Taxable Income or Separate Group Taxable Loss of each Group included in the Consolidated Federal Return. Each Group included in the Consolidated Federal Return shall bear its Federal Separate Group Tax Liability, if any. For purposes of such calculation, the deduction for state and local taxes to which each Group is entitled will be determined in a manner consistent with Section 4 of this Agreement.

(ii) If the MSCI Group included in the Consolidated Federal Return incurs a Separate Group Taxable Loss, MS shall pay to the MSCI Group (A) the amount, if any, by which the federal income taxes payable with respect to the Consolidated Federal Return are actually reduced by reason of the MSCI Group’s Separate Group Taxable Loss and (B) any Refund of federal income taxes or other federal income Tax Benefit attributable to such Separate Group Taxable Loss that is Actually Realized, in each case as determined by MS in its sole discretion (including that any Tax Benefits of the MS Group shall be fully utilized before utilizing any Tax Benefits of the MSCI Group). To the extent the MSCI Group receives a payment or credit from

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MS in respect of a Separate Company Taxable Loss pursuant to this Section 3(b)(ii), such loss shall not be carried forward or carried back by the MSCI Group for purposes of determining Separate Group Taxable Income or Separate Group Taxable Loss in any other Taxable period (or portion thereof). To the extent the MSCI Group does not receive a payment or credit from MS in respect of a Separate Group Taxable Loss pursuant to this Section 3(b)(ii), such loss may be carried forward or carried back, subject to any applicable limitation with respect to carry forward or carry back losses, by the MSCI Group for purposes of determining Separate Group Taxable Income or Separate Group Taxable Loss in another Taxable period (or portion thereof).

(iii) If the MSCI Group included in the Consolidated Federal Return has a foreign Tax credit or other Tax credit that it is unable to use in its calculation of Federal Separate Group Tax Liability (other than an AMT credit), MS shall pay to the MSCI Group (A) the amount, if any, by which the federal income taxes payable with respect to the Consolidated Federal Return is actually reduced by reason of the MSCI Group’s Tax credit and (B) any Refund of federal income taxes or other federal income Tax Benefit attributable to such Tax credit that is Actually Realized, in each case as determined by MS in its sale discretion (including that any Tax Benefits of the MS Group shall be fully utilized before utilizing any Tax Benefits of the MSCI Group). To the extent the MSCI Group receives a payment or credit from MS in respect of a Tax credit pursuant to this Section 3(b)(iii), the MSCI Group’s Federal Separate Group Tax Liability will be adjusted to reflect the fact that the MSCI Group has previously received the benefit of such credit. To the extent the MSCI Group does not receive a payment or credit from MS in respect of a Tax credit pursuant to this Section 3(b)(iii), such Tax credit may be carried forward or carried back, subject to any applicable limitation with respect to carry forward or carry back of Tax credits, by the MSCI Group for purposes of calculating its Separate Group Tax Liability in another Taxable period (or portion thereof).

(iv) In the event a Consolidated Group incurs an AMT liability with respect to any Taxable period (or portion thereof), MS shall be solely responsible for such liability. Any Tax Benefit arising from the utilization of a consolidated federal AMT credit shall be for the sale benefit of MS.

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4. State and Local Income Taxes.

(a) Return Filing.

(i) MS shall prepare and file, or cause to be prepared and filed, Consolidated State Returns for which a Consolidated Group is required or permitted to file a Consolidated State Return using, inter alia, information provided by MSCI. MSCI shall provide MS with all necessary information to file a Consolidated State Return not later than 45 days after MS’s fiscal year-end and shall respond promptly to all information requests, but in no event more than two business days following a request. Each member of the Consolidated Group shall execute and file such consents, elections and other documents as may be required or appropriate for the filing of such Consolidated State Returns. All Tax elections shall be made at the discretion of MS provided, however, that MSCI shall be entitled to direct MS to make any and all Tax elections that exclusively affect the MSCI Group, subject to MS’s consent. All Tax computations performed on a combined, consolidated or unitary basis will be performed or approved by MS. MS shall not change any method of accounting that relates exclusively to the MSCI Group for any Tax purpose if such change adversely affects the MSCI Group unless such change is required by law. MS shall notify and discuss with MSCI prior to the filing of a Consolidated State Return any potential material differences in the information provided by MSCI to be used in the preparation of such Consolidated State Return and the position MS intends to take on such Consolidated State Return.

(ii) MS shall pay, or cause to be paid, and, subject to the provisions of Section 4(b), shall be responsible for, any and all income taxes due or required to be paid with respect to, or required to be reported on, any such Consolidated State Return.

(iii) In the event a Consolidated State Return is not filed, each relevant member of the MS Group and MSCI Group shall be responsible for (A) filing its own Return as a separate entity, or its own Return in respect of state and local income Taxes relating to a group consisting solely of members of the MS Group or members of the MSCI Group, as the case may be, on behalf of the separate group, in each case including requests for extension, as if this Agreement were not in effect and (B) making Tax payments (including estimated Tax payments, if necessary). Each such member filing a Return as a separate entity shall be entitled to any Tax Benefit and shall be liable for any Tax burden resulting from the filing of such separate Return.

(b) Allocated Tax Charge.

(i) MS shall be responsible for calculating the Separate Group Taxable Income or Separate Group Taxable Loss

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for each Group included in a Consolidated State Return. Each Group included in a Consolidated State Return shall bear its State Separate Group Tax Liability, if any.

(ii) If the MSCI Group included in a Consolidated State Return incurs a Separate Group Taxable Loss, MS shall pay, or shall cause to be paid, to the MSCI Group (A) the amount, if any, by which the state or local income taxes reflected on such Return are actually reduced by reason of the MSCI Group’s Separate Group Taxable Loss and (B) any Refund of state or local income taxes or other state or local income Tax Benefit attributable to such Separate Group Taxable Loss that is Actually Realized, in each case as determined by MS in its sole discretion (including that any Tax Benefits of the MS Group shall be fully utilized before utilizing any Tax Benefits of the MSCI Group). To the extent the MSCI Group receives a payment or credit from MS in respect of a Separate Group Taxable Loss pursuant to this Section 4(b)(ii), such loss shall not be carried forward or carried back by the MSCI Group for purposes of determining Separate Group Taxable Income or Separate Group Taxable Loss in any other Taxable period (or portion thereof). To the extent the MSCI Group does not receive a payment or credit from MS in respect of a Separate Group Taxable Loss pursuant to this Section 4(b)(ii), such loss may be carried forward or carried back, subject to any applicable limitation with respect to carry forward or carry back losses, by the MSCI Group for purposes of determining Separate Group Taxable Income or Separate Group Taxable Loss in another Taxable period (or portion thereof).

(iii)