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                                                                     EXHIBIT 5.1

                            [BAKER BOTTS LETTERHEAD]

                                 August 29, 2001

Affiliated Computer Services, Inc.
2828 North Haskell Avenue
Dallas, Texas 75204

Ladies and Gentlemen:

     We have acted as counsel for Affiliated Computer Services, Inc., a Delaware
corporation (the "Company"), in connection with the Registration Statement on
Form S-3 (the "Registration Statement") filed on this date by the Company ACS
Trust I and ACS Trust II, each a statutory business trust formed under the laws
of the State of Delaware (the "Trusts", and together with the Company, the
"Registrants"), with the Securities and Exchange Commission (the "Commission")
under the Securities Act of 1933, as amended (the "Securities Act"). The
Registration Statement relates to the proposed issuance and sale from time to
time pursuant to Rule 415 under the Securities Act of up to $1,500,000,000
aggregate initial offering price of (a) the Company's senior debt securities
(the "Senior Debt Securities"), (b) the Company's subordinated debt securities
(the "Subordinated Debt Securities"), (c) shares of Class A Common Stock, par
value $.01 per share, of the Company (the "Common Stock"), (d) shares of
preferred stock of the Company (the "Preferred Stock"), (e) depositary shares of
the Company (the "Depositary Shares"), (f) warrants of the Company to purchase
other securities (the "Warrants"), (g) preferred securities of the Trusts (the
"Trust Preferred Securities") and (h) the Company's guarantees with respect to
the Trust Preferred Securities (each, a "Guarantee" and, collectively, the
"Guarantees"). The Senior Debt Securities, the Subordinated Debt Securities, the
Common Stock, the Preferred Stock, the Depositary Shares, the Warrants, the
Trust Preferred Securities and the Guarantees may be hereinafter referred to as
the "Securities."

     Each series of the Senior Debt Securities will be issued pursuant to an
indenture to be entered into in connection with the first series of Senior Debt
Securities thereunder between the Company and U.S. Trust Company of Texas, N.A.,
as Trustee (the "Senior Indenture"), and each series of the Subordinated Debt
Securities will be issued pursuant to an indenture to be entered into in
connection with the first series of Subordinated Debt Securities issued
thereunder between the Company and U.S. Trust Company of Texas, N.A., as Trustee
(the "Subordinated Indenture"), as each such indenture will be supplemented, in
connection with the issuance of each such series, by a supplemental indenture or
other appropriate action of the Company creating such series (each, a
"Supplemental Indenture"). Each Guarantee will be issued pursuant to a guarantee

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agreement to be entered into between the Company and Wilmington Trust Company,
as guarantee trustee thereunder (each, a "Guarantee Agreement" and,
collectively, the "Guarantee Agreements"), at the time any Trust Preferred
Securities are issued by either Trust.

     In furnishing this opinion, we have examined and relied upon originals or
copies, certified or otherwise identified to our satisfaction, of the Amended
and Restated Certificate of Incorporation and Bylaws of the Company, as amended
to date (together, the "Charter Documents"), resolutions adopted by the Board of
Directors of the Company (the Board of Directors, or to the extent permitted by
Section 141 of the Delaware General Corporation Law, a duly constituted and
acting committee thereof, being referred to herein as the "Board"), the Senior
Indenture, the Subordinated Indenture and the Guarantee Agreement filed as
exhibits to the Registration Statement, corporate records of the Company,
including minute books of the Company, certificates of public officials and of
representatives of the Company and the Trusts, statutes and other instruments
and documents as we have deemed necessary or appropriate to form a basis for the
opinions hereinafter expressed.

     In connection with this opinion, we have assumed: (a) the genuineness of
all signatures on all documents examined by us; (b) the authenticity of all
documents submitted to us as originals and the conformity to the originals of
all documents submitted to us as copies; (c) the Registration Statement, and any
amendments thereto (including post-effective amendments), will have become
effective under the Securities Act; (d) a prospectus supplement will have been
filed with the Commission describing the Securities offered thereby; (e) all
Securities will be issued and sold in compliance with applicable federal and
state securities laws and in the manner stated in the Registration Statement and
the applicable prospectus supplement; (f) a definitive purchase, underwriting or
similar agreement with respect to any Securities offered will have been duly
authorized and validly executed and delivered by the Company and the other
parties thereto; (g) any securities issuable upon conversion, exchange,
redemption or exercise of any Securities being offered will be duly authorized,
created and, if appropriate, reserved for issuance upon such conversion,
exchange, redemption or exercise; and (h) with respect to shares of Common Stock
or Preferred Stock offered, there will be sufficient shares of Common Stock or
Preferred Stock authorized under the Company's Charter Documents and not
otherwise reserved for issuance.

     On the basis of the foregoing, and subject to the assumptions, limitations
and qualifications set forth herein, we are of the opinion that:

     1. With respect to a series of Senior Debt Securities, when (a) the Senior
Indenture has been duly authorized and validly executed and delivered by the
parties thereto, (b) any applicable Supplemental Indenture relating to such
series has been duly authorized and validly executed and delivered by each of
the parties thereto, (c) the Board has taken all necessary corporate action to
approve and establish the terms of such series and to authorize and approve the
issuance thereof, the terms of the offering thereof and related matters, and (d)
the Senior Debt Securities of such series have been duly executed,
authenticated, issued and delivered in accordance with the Senior Indenture, any
applicable Supplemental Indenture relating to such series and the applicable
definitive purchase, underwriting or similar agreement approved by the Board in
exchange for payment of the consideration therefor provided for therein, the
Senior Debt Securities of such series will

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constitute legal, valid and binding obligations of the Company, enforceable
against the Company in accordance with their terms, except as the enforceability
thereof may be subject to the effect of (i) bankruptcy, insolvency,
reorganization, moratorium, fraudulent conveyance or other laws relating to or
affecting creditors' rights generally and (ii) general principles of equity
(regardless of whether such enforceability is considered in a proceeding in
equity or at law).

     2. With respect to a series of Subordinated Debt Securities, when (a) the
Subordinated Indenture has been duly authorized and validly executed and
delivered by the parties thereto, (b) any applicable Supplemental Indenture
relating to such series has been duly authorized and validly executed and
delivered by each of the parties thereto, (c) the Board has taken all necessary
corporate action to approve and establish the terms of such series and to
authorize and approve the issuance thereof, the terms of the offering thereof
and related matters, and (d) the Subordinated Debt Securities of such series
have been duly executed, authenticated, issued and delivered in accordance with
the Subordinated Indenture, any applicable Supplemental Indenture relating to
such series and the applicable definitive purchase, underwriting or similar
agreement approved by the Board in exchange for payment of the consideration
therefor provided for therein, the Subordinated Debt Securities of such series
will constitute legal, valid and binding obligations of the Company, enforceable
against the Company in accordance with their terms, except as the enforceability
thereof is subject to the effect of (i) bankruptcy, insolvency, reorganization,
moratorium, fraudulent conveyance or other laws relating to or affecting
creditors' rights generally and (ii) general principles of equity (regardless of
whether such enforceability is considered in a proceeding in equity or at law).

     3. With respect to shares of Common Stock, when (a) the Board has taken all
necessary corporate action to approve the issuance thereof and the terms of the
offering of shares of Common Stock and related matters, and (b) certificates
representing the shares of Common Stock have been duly executed, countersigned,
registered and delivered, either (i) in accordance with the applicable
definitive purchase, underwriting or similar agreement approved by the Board in
exchange for payment of the consideration therefor (not less than the par value
of the Common Stock) provided for therein, or (ii) upon conversion, exchange,
redemption or exercise of any other Security, in accordance with the terms of
such Security or the instrument governing such Security providing for such
conversion, exchange, redemption or exercise as approved by the Board, for the
consideration approved by the Board (not less than the par value of the Common
Stock), the shares of Common Stock will be duly authorized, validly issued,
fully paid and non-assessable.

     4. With respect to shares of Preferred Stock, when (a) the Board has taken
all necessary corporate action to approve and establish the terms of the shares
of Preferred Stock, to approve the issuance thereof and the terms of the
offering thereof and related matters, including the adoption of a Certificate of
Designation relating to such Preferred Stock (a "Certificate of Designation"),
and such Certificate of Designation has been filed with the Secretary of State
of the State of Delaware, and (b) certificates representing the shares of
Preferred Stock have been duly executed, countersigned, registered and
delivered, either (i) in accordance with the applicable definitive purchase,
underwriting or similar agreement approved by the Board in exchange for payment
of the consideration therefor (not less than the par value of the Preferred
Stock) provided for therein, or (ii) upon conversion, exchange, redemption or
exercise of any

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other Security, in accordance with the terms of such Security or the instrument
governing such Security providing for such conversion, exchange, redemption or
exercise as approved by the Board, for the consideration approved by the Board
(not less than the par value of the Preferred Stock), the shares of Preferred
Stock will be duly authorized, validly issued, fully paid and non-assessable.

     5. With respect to the Depositary Shares, when (a) the Board has taken all
necessary corporate action to approve the issuance and terms of the Depositary
Shares, the terms of the offering thereof and related matters, including the
adoption of a Certificate of Designation relating to the Preferred Stock
underlying the Depositary Shares and the filing of the Certificate of
Designation with the Secretary of State of Delaware, (b) the depositary
agreement or agreements relating to the Depositary Shares and the related
depositary receipts have been duly authorized and validly executed and delivered
by the Company and the depositary appointed by the Company, (c) the shares of
Preferred stock underlying the Depositary Shares have been duly and validly
issued and deposited with a bank or trust company (which meets the requirements
for the depositary set forth in the Registration Statement) under the applicable
depositary agreements, and (d) the depositary receipts representing the
Depositary Shares have been duly executed, countersigned, registered and
delivered in accordance with the appropriate depositary agreement approved by
the Board upon payment of the consideration therefore provided for therein, the
Depositary Shares will be legally issued.

     6. With respect to Warrants, when (a) the Board has taken all necessary
corporate action to approve the creation of and the issuance and terms of the
Warrants, the terms of the offering thereof and related matters, (b) the warrant
agreement or agreements relating to the Warrants have been duly authorized and
validly executed and delivered by the Company and the warrant agent appointed by
the Company, and (c) the Warrants or certificates representing the Warrants have
been duly executed, countersigned, registered and delivered in accordance with
the appropriate warrant agreement or agreements and the applicable definitive
purchase, underwriting or similar agreement approved by the Board in exchange
for payment of the consideration therefor provided for therein, the Warrants
will be duly authorized and validly issued and will constitute legal, valid and
binding obligations of the Company, enforceable against the Company in
accordance with their terms, except as the enforceability thereof may be subject
to the effect of (i) bankruptcy, insolvency, reorganization, moratorium,
fraudulent conveyance or other laws relating to or affecting creditors' rights
generally and (ii) general principles of equity (regardless of whether such
enforceability is considered in a proceeding in equity or at law).

     7. With respect to each Guarantee Agreement, when (a) such Guarantee
Agreement has been duly authorized, validly executed and delivered by each of
the parties thereto, (b) the Company has received the purchase price for the
Trust Preferred Securities to which such Guarantee Agreement relates and such
Trust Preferred Securities have been duly and validly issued, and (c) the Board
has taken all necessary corporate action to approve the Guarantee and the
issuance thereof and related matters, such Guarantee Agreement will constitute
the legal, valid and binding obligation of the Company, enforceable against the
Company in accordance with its terms, except as the enforceability thereof is
subject to the effect of (i) bankruptcy, insolvency,

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reorganization, moratorium, fraudulent conveyance or other laws relating to or
affecting creditors' rights generally and (ii) general principles of equity
(regardless of whether such enforceability is considered in a proceeding in
equity or at law).

     The foregoing opinions are qualified to the extent that the enforceability
of any document, instrument or Security may be limited by or subject to (i)
bankruptcy, insolvency, fraudulent transfer or conveyance, reorganization,
moratorium or other similar laws relating to or affecting creditors' rights
generally, and general equitable or public policy principles, and (ii) with
respect to any Securities denominated in a currency other than United States
dollars, the requirement that a claim (or a foreign currency judgment in respect
of such a claim) with respect to such Securities be converted to United States
dollars at a rate of exchange prevailing on a date determined pursuant to
applicable law or governmental authority.

     We express no opinions concerning (i) the validity or enforceability of any
provisions contained in any agreement or instrument pertaining to any Security
that purport to waive or not give effect to rights to notices, defenses,
subrogation or other rights or benefits that cannot be effectively waived under
applicable law or (ii) the enforceability of indemnification provisions to the
extent they purport to relate to liabilities resulting from or based upon
negligence or any violation of federal or state securities or blue sky laws.

     The foregoing opinions are limited in all respects to the Delaware General
Corporation Law and the laws of the States of New York and Texas and federal law
of the United States of America, and we do not express any opinions as to the
laws of any other jurisdiction.

     We hereby consent to the reference to our Firm under the caption "Legal
Matters" in the Registration Statement. In giving such consent, we do not
thereby concede that we are within the category of persons whose consent is
required under Section 7 of the Securities Act or the rules and regulations of
the Commission promulgated thereunder.

                                       Very truly yours,

                                       /s/ BAKER BOTTS L.L.P.




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