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                                                                     EXHIBIT 5.1

                        BROBECK, PHLEGER & HARRISON LLP
                             4801 Plaza on the Lake
                              Austin, Texas 78746

                                November 2, 2000


i2 Technologies, Inc.
One i2 Place
11701 Luna Road
Dallas, Texas  75234
(469) 357-1000

                  Re:      i2 Technologies, Inc. Registration Statement on
                           Form S-3 for 109,514 Shares of Common Stock

Ladies and Gentlemen:

         We have acted as counsel to i2 Technologies, Inc., a Delaware
corporation (the "Company"), in connection with the sale by a stockholder of the
Company of up to 109,514 shares of the Company's Common Stock (collectively, the
"Shares"), pursuant to the Company's Registration Statement on Form S-3 (the
"Registration Statement") filed with the Securities and Exchange Commission
under the Securities Act of 1933, as amended (the "Act").

         This opinion is being furnished in accordance with the requirements of
Item 16 of Form S-3 and Item 601(b)(5)(i) of Regulation S-K.

         We have reviewed the Company's charter documents and the corporate
proceedings taken by the Company in connection with the issuance and sale of the
Shares. Based on such review, we are of the opinion that the Shares are duly
authorized, validly issued, fully paid and nonassessable.

         We consent to the filing of this opinion letter as Exhibit 5.1 to the
Registration Statement and to the reference to this firm under the caption
"Legal Matters" in the prospectus which is part of the Registration Statement.
In giving this consent, we do not thereby admit that we are within the category
of persons whose consent is required under Section 7 of the Act, the rules and
regulations of the Securities and Exchange Commission promulgated thereunder or
Item 509 of Regulation S-K.

         This opinion letter is rendered as of the date first written above and
we disclaim any obligation to advise you of facts, circumstances, events or
developments which hereafter may be brought to our attention and which may
alter, affect or modify the opinion expressed herein. Our opinion is expressly
limited to the matters set forth above and we render no opinion, whether by
implication or otherwise, as to any other matters relating to the Company or the
Shares.

                                        Very truly yours,

                                    /s/ BROBECK, PHLEGER & HARRISON LLP