<PAGE>   1
                                                                     Exhibit 3.1

                                    RESTATED

                          CERTIFICATE OF INCORPORATION

                                       OF

                              i2 TECHNOLOGIES, INC.

                            (A DELAWARE CORPORATION)


    i2 Technologies, Inc., a corporation organized and existing under the
Delaware General Corporation Law, hereby certifies as follows:

1.       That this corporation was originally incorporated on January 9, 1992
         under the name Intellection, Inc., pursuant to the Delaware General
         Corporation Law.

2.       Pursuant to Section 245 of the Delaware General Corporation Law, this
         Restated Certificate of Incorporation has been duly adopted and
         restates and integrates and does not further amend the provisions of
         the Certificate of Incorporation of this corporation as heretofore
         amended or supplemented, and there is no discrepancy between those
         provisions and the provisions of this Restated Certificate of
         Incorporation, except that all references to Articles herein have been
         revised to reflect the deletion of Article Fifth of the Certificate of
         Incorporation (Incorporator).

3.       The text of the Certificate of Incorporation of this corporation is
         hereby restated in its entirety to read as follows:

    FIRST: The name of the corporation is i2 Technologies, Inc. (the
"Corporation").

    SECOND: The address of the Corporation's registered office in the State of
Delaware is 1209 Orange Street, Wilmington, Delaware 19801. The name of its
registered agent at such address is The Corporation Trust Company.

    THIRD: The purpose of the Corporation is to engage in any lawful act or
activity for which corporations may be organized under the General Corporation
Law of Delaware.

    FOURTH:

A.       The total number of shares which the Corporation shall have authority
         to issue is TWO HUNDRED AND FIVE MILLION (205,000,000) shares of
         capital stock.

B.       Of such authorized shares, TWO HUNDRED MILLION (200,000,000) shares
         shall be designated "Common Stock", and have a par value of $.00025.

C.       Of such authorized shares, FIVE MILLION (5,000,000) shares shall be
         designated "Preferred Stock", and have a par value of $.001. The
         Preferred Stock may be issued from time to time in one or more series.
         The Board of Directors of the Corporation is authorized to determine or
         alter the powers, preferences and rights and the qualifications,
         limitations or restrictions granted to or imposed upon any wholly
         unissued series of Preferred Stock, and within the limitations or
         restrictions stated in any resolution or resolutions of the Board of
         Directors originally fixing the number of shares constituting any
         series, to increase or decrease (but not below the number of shares of
         any such series then outstanding) the number of shares of any such
         series subsequent to the issuance of shares of that series, to
         determine the designation of any series, and to fix the number of
         shares of any series. In case the number of shares of any series shall
         be so decreased, the shares constituting such decrease shall resume the
         status which they had prior to the adoption of the resolution
         originally fixing the number of shares of such series.

    FIFTH: The Corporation is to have perpetual existence.
<PAGE>   2
    SIXTH: Elections of directors need not be by written ballot unless a
stockholder demands election by written ballot at the meeting and before voting
begins.

    SEVENTH:

A.       At each annual meeting of stockholders, directors of the Corporation
         shall be elected to hold office until the expiration of the term for
         which they are elected, and until their successors have been duly
         elected and qualified; except that if any such election shall not be so
         held, such election shall take place at a stockholders' meeting called
         and held in accordance with the Delaware General Corporation Law. At
         the annual meeting of stockholders (the "First Public Company Annual
         Meeting") following the closing of a public offering of the
         Corporation's Capital Stock pursuant to an effective registration
         statement filed under the Securities Act of 1933, as amended (a "Public
         offering"), the directors of the Corporation shall be divided into
         three classes as nearly equal in size as is practicable, hereby
         designated Class I, Class II and Class III. The term of office of the
         initial Class I directors shall expire at the next succeeding annual
         meeting of stockholders, the term of office of the initial Class II
         directors shall expire at the second succeeding annual meeting of
         stockholders and the term of office of the initial Class III directors
         shall expire at the third succeeding annual meeting of the
         stockholders. For the purposes hereof, the initial Class I, Class II
         and Class III directors shall be those directors so designated and
         elected at the First Public Company Annual Meeting. At each annual
         meeting after the First Public Company Annual Meeting, directors to
         replace those of a Class whose terms expire at such annual meeting
         shall be elected to hold office until the third succeeding annual
         meeting and until their respective successors shall have been duly
         elected and qualified. If the number of directors is hereafter changed,
         any newly created directorships or decrease in directorships shall be
         so apportioned among the classes as to make all classes as nearly equal
         in number as is practicable.

B.       Vacancies occurring on the Board of Directors for any reason may be
         filled by vote of a majority of the remaining members of the Board of
         Directors, although less than a quorum, at a meeting of the Board of
         Directors. A person so elected by the Board of Directors to fill a
         vacancy shall hold office until the next succeeding annual meeting of
         stockholders of the Corporation and until his or her successor shall
         have been duly elected and qualified.

    EIGHTH: The number of directors which constitute the whole Board of
Directors of the Corporation shall be designated in the Bylaws of the
Corporation.

    NINTH: In furtherance and not in limitation of the powers conferred by
statute, the Board of Directors is expressly authorized to make, alter, amend or
repeal the Bylaws of the Corporation.

    TENTH: To the fullest extent permitted by the Delaware General Corporation
Law as the same exists or as it may hereafter be amended, no director of the
Corporation shall be personally liable to the Corporation or its stockholders
for monetary damages for breach of fiduciary duty as a director. Neither any
amendment nor repeal of this Article, nor the adoption of any provision of this
Certificate of Incorporation inconsistent with this Article, shall eliminate or
reduce the effect of this Article in respect of any matter occurring, or any
cause of action, suit or claim that, but for this Article, would accrue or
arise, prior to such amendment, repeal or adoption of an inconsistent provision.

    ELEVENTH: At the election of directors of the Corporation, each holder of
stock of any class of series shall be entitled to as many votes as shall equal
the number of votes which (except for such provision as to cumulative voting) he
would be entitled to cast for the election of directors with respect to his
shares of stock multiplied by the number of directors to be elected by him, and
he may cast all of such votes for a single director or may distribute them among
the number to be voted for, or for any two or more of them as he may see fit, so
long as the name of the candidate for director shall have been placed in
nomination prior to the voting and the stockholder, or any other holder of the
same class or series of stock, has given notice at the meeting prior to the
voting of the intention to cumulate votes; provided that, notwithstanding the
above and any provision contained in this Certificate of Incorporation to the
contrary, effective upon a Public Offering, the holders of stock of any class or
series shall no longer be entitled to such cumulative
<PAGE>   3
voting rights.

    TWELFTH: Meetings of stockholders may be held within or without the State of
Delaware, as the Bylaws may provide. The books of the Corporation may be kept
(subject to any provision contained in the statutes) outside of the State of
Delaware at such place or places as may be designated from time to time by the
Board of Directors or in the Bylaws of the Corporation.

    THIRTEENTH: Effective upon the closing of a Public Offering, stockholders of
the Corporation may not take action by written consent in lieu of a meeting but
must take any actions at a duly called annual or special meeting.

    FOURTEENTH: Notwithstanding any other provisions of this Certificate of
Incorporation or any provision of law which might otherwise permit a lesser vote
or no vote, but in addition to any affirmative vote of the holders of the
capital stock required by law or this Certificate of Incorporation, the
affirmative vote of the holders of at least two-thirds (2/3) of the combined
voting power of all of the then-outstanding shares of the Corporation entitled
to vote shall be required to alter, amend or repeal Articles SEVENTH, ELEVENTH,
THIRTEENTH or FOURTEENTH or any provision thereof, unless such amendment shall
be approved by a majority of the directors of the Corporation not affiliated or
associated with any person or entity holding (or which has announced an
intention to obtain) 26% or more of the voting power of the Corporation's
outstanding capital stock.

    FIFTEENTH: The Corporation reserves the right to amend, alter, change or
repeal any provision contained in this Certificate of Incorporation, in the
manner now or hereafter prescribed by statute, and all rights conferred upon
stockholders herein are granted subject to this reservation.

    IN WITNESS WHEREOF, i2 Technologies, Inc. has caused this Restated
Certificate of Incorporation to be signed by its Chief Financial Officer this
6th day of November, 1998.

                                   i2 Technologies, Inc.


                                   By: /S/ DAVID F. CARY
                                      -----------------------------------------
                                        David F. Cary
                                        Chief Financial Officer
<PAGE>   4
                            CERTIFICATE OF AMENDMENT

                                       OF

                                    RESTATED

                          CERTIFICATE OF INCORPORATION

                                       OF

                              i2 TECHNOLOGIES, INC.

i2 TECHNOLOGIES, INC., a corporation organized and existing under the laws of
the State of Delaware (the "Corporation"), HEREBY CERTIFIES:

    FIRST: That a meeting of the directors of the Corporation held on April 11,
1999, the directors of the Corporation adopted resolutions approving and
declaring advisable the following amendment to the Corporation's Restated
Certificate of Incorporation:

                           BE IT RESOLVED, that, subject to the approval of the
         Corporation's stockholders, the Restated Certificate of Incorporation
         be amended by amending paragraphs A and B of the Article thereof
         numbered "FOURTH" so that, as amended, said paragraphs shall read in
         full as follows:

                           "A. The total number of shares which the Corporation
                  shall have authority to issue is FIVE HUNDRED AND FIVE MILLION
                  (505,000,000) shares of capital stock.

                           B. Of such authorized shares FIVE HUNDRED MILLION
                  (500,000,000) shares shall be designated "Common Stock," and
                  have a par value of $.00025."

    SECOND: That at a meeting of the stockholders of the Corporation called and
held upon notice in accordance with the provisions of Section 222 of the General
Corporation Law of the State of Delaware, the required percentage of shares of
stock of the Corporation voted in favor of said amendment.

    THIRD: That said amendment was duly adopted in accordance with the
provisions of Section 242 of the General Corporation Law of the State of
Delaware.

    IN WITNESS WHEREOF, the undersigned officer of i2 Technologies, Inc. has
hereunto set his hand this 31st day of August 1999.

                             i2 Technologies, Inc.


                             By: /S/ WILLIAM M. BEECHER
                                -----------------------------------------
                                  William M. Beecher
                                  Executive Vice President and
                                  Chief Financial Officer
<PAGE>   5
                            CERTIFICATE OF AMENDMENT

                                       OF

                                    RESTATED

                          CERTIFICATE OF INCORPORATION

                                       OF

                              i2 TECHNOLOGIES, INC.

    i2 TECHNOLOGIES, INC., a corporation organized and existing under the laws
of the State of Delaware (the "Corporation"), HEREBY CERTIFIES:

    FIRST: That by unanimous written consent of the directors of the Corporation
dated October 17, 2000, the directors of the Corporation adopted resolutions
approving and declaring advisable the following amendment to the Corporation's
Restated Certificate of Incorporation:

                           BE IT RESOLVED, that subject to the approval of the
         Corporation's stockholders, the Restated Certificate of Incorporation
         of the Corporation be amended by amending paragraphs A and B of the
         Article thereof numbered "FOURTH" so that, as amended, said paragraphs
         shall read in full as follows:

                           "A. The total number of shares which the Corporation
                  shall have authority to issue is TWO BILLION, FIVE MILLION
                  (2,005,000,000) shares of capital stock.

                           B. Of such authorized shares, TWO BILLION
                  (2,000,000,000) shares shall be designated "Common Stock," and
                  have a par value of $.00025."

    SECOND: That at a meeting of the stockholders of the Corporation called and
held upon notice in accordance with the provisions of Section 222 of the General
Corporation Law of the State of Delaware, the required percentage of shares of
stock of the Corporation voted in favor of said amendment.

    THIRD: That said amendment was duly adopted in accordance with the
provisions of Section 242 of the General Corporation Law of the State of
Delaware.

    IN WITNESS WHEREOF, the undersigned officer of i2 Technologies, Inc. has
hereunto set his hand this 29th day of November 2000.

                                  i2 Technologies, Inc.


                                  By: /S/ ROBERT C. DONOHOO
                                     -----------------------------------------
                                       Robert C. Donohoo,
                                       Corporate Secretary