<PAGE>

                                                                   EXHIBIT 10.21

                              VIGNETTE CORPORATION
                          NOTICE OF STOCK OPTION GRANT

You have been granted the following option to purchase shares of the Common
Stock of Vignette Corporation (the "Corporation"):

     Name of Optionee:                 Michael Crosno

     Total Number of Shares:           1,850,000

     Type of Option:                   Nonstatutory Stock Option

     Exercise Price Per Share:         $1.3700

     Date of Grant:                    December 9, 2002

     Vesting Commencement Date:        December 2, 2002

     Vesting                           Schedule: This option becomes exercisable
                                       in equal increments. The first 25% of the
                                       Shares subject to this option shall
                                       become exercisable when you complete
                                       twelve (12) months of Service from the
                                       Vesting Commencement Date. An additional
                                       6.25% of the Shares subject to this
                                       option shall become exercisable when you
                                       complete each quarter of Service
                                       thereafter.

     Expiration                        Date: 8 years from Grant Date; however,
                                       this option will expire earlier if your
                                       Service terminates earlier, as described
                                       in the Stock Option Agreement.

Nothing in this Notice or in the Stock Option Agreement shall confer upon you
any right to continue in Service for any period of specific duration or
interfere with or otherwise restrict in any way your rights or the rights of the
Corporation (or any parent or subsidiary employing or retaining you), which
rights are hereby expressly reserved by each, to terminate your Service at any
time for any reason, with or without cause.

You further agree that the Corporation may deliver by email all documents
relating to this option (including, without limitation, prospectuses required by
the Securities and Exchange Commission) and all other documents that the
Corporation is required to deliver to its security holders (including, without
limitation, annual reports and proxy statements). You also agree that the
Corporation may deliver these documents by posting them on a web site maintained
by the Corporation or by a third party under contract with the Corporation. If
the Corporation posts these documents on a web site, it will notify you by
email.

By accepting this option, you and the Corporation agree that this option is
granted under and governed by the terms and conditions of the Stock Option
Agreement, which is attached to and made a part of this document.

OPTIONEE:                              VIGNETTE CORPORATION

                                       By:
----------------------------------        ------------------------------------

                                       Title:
                                             ---------------------------------

<PAGE>

                              VIGNETTE CORPORATION
                             STOCK OPTION AGREEMENT

Tax Treatment       This option is intended to be an incentive stock option
                    under section 422 of the Internal Revenue Code or a
                    nonstatutory stock option, as provided in the Notice of
                    Stock Option Grant.

Vesting             This option becomes exercisable in installments, as shown in
                    the Notice of Stock Option Grant. In addition, this option
                    becomes exercisable in full if either of the following
                    events occurs:

                    o    Your Service (as defined below) terminates because of
                         death, or

                    o    The Corporation is subject to a "Change in Control" (as
                         defined below) before your Service terminates, and you
                         are subject to an "Involuntary Termination" (as defined
                         below) within 18 months after the Change in Control.

                    This option will in no event become exercisable for
                    additional shares after your service as an employee,
                    consultant or outside director of the Corporation or a
                    parent or subsidiary of the Corporation ("Service") has
                    terminated for any reason. It is intended that the exercise
                    schedule for this option is commensurate with a full-time
                    work schedule. For possible adjustments that may be made by
                    the Corporation, see the Section below entitled "Leaves of
                    Absence and Part-Time Work."

Change in Control   In the event of a Change in Control, then the vesting of
                    this option will automatically accelerate so that this
                    option will immediately before the effective date of the
                    Change in Control, become fully exercisable for all of the
                    shares of Common Stock at the time subject to this option
                    and may be exercised for any or all of those shares as
                    fully-vested shares of Common Stock. However, this option
                    will not so accelerate if and to the extent this option is,
                    in connection with the Change in Control, either to be
                    assumed by the successor corporation (or its parent) or to
                    be replaced with a comparable option for shares of the
                    capital stock of the successor corporation (or its parent).
                    The determination of option comparability will be made by
                    the Corporation's Board of Directors, and its determination
                    will be final, binding and conclusive.

                    Change in Control is defined in the Corporation's 1999
                    Equity Incentive Plan.

                                       2

<PAGE>

Involuntary         If the option is assumed by the successor corporation (or
Termination         its parent) and you experience an Involuntary Termination
                    within eighteen months following a Change in Control, the
                    vesting of this option will automatically accelerate so that
                    this option will, immediately before the effective date of
                    the Involuntary Termination, become fully exercisable for
                    all of the shares of Common Stock at the time subject to
                    this option and may be exercised for any or all of those
                    shares as fully-vested shares of Common Stock.

                    Involuntary Termination is defined in the Corporation's 1999
                    Equity Incentive Plan.

Limitation on       This provision shall apply to you only if, on an after-tax
Acceleration        basis, you would receive more value under this Agreement
                    after the application of this provision than before the
                    application of this provision. For this purpose, "after-tax
                    basis" shall mean a calculation taking into account all
                    federal and state income and excise taxes imposed on you,
                    including (without limitation) the excise tax described in
                    section 4999 of the Internal Revenue Code (the "Code"). If
                    this provision is applicable, it shall supersede any
                    conflicting provision of this Agreement.

                    All calculations required by this provision shall be
                    performed by the independent auditors retained by the
                    Corporation most recently prior to the Change in Control
                    (the "Auditors"), based on information supplied by the
                    Corporation and you, and shall be binding on the Corporation
                    and you. All fees and expenses of the Auditors shall be paid
                    by the Corporation.

                    A reduction in the acceleration resulting from application
                    of the provisions of this Agreement relating to Change in
                    Control or Involuntary Termination shall be made if the
                    Auditors determine that on an after-tax basis, the value of
                    such acceleration would be greater after the application of
                    such a reduction.

                    If a reduction is to be effected, it will be applied as
                    follows: vesting shall not be accelerated with respect to
                    one or more shares under this Agreement until the reduced
                    number of shares would result in no portion of the
                    compensation payable to you being subject to excise tax
                    under Section 4999 of the Code; provided that you may
                    request that other parachute payments to be made to you by
                    the Company be reduced in lieu of a reduction in the
                    acceleration under this Agreement, but no change in the
                    timing of any payment or transfer shall be made without the
                    Corporation's consent. Section 18 of the Corporation's 1999
                    Equity Incentive Plan does not apply to this option.

                                       3

<PAGE>

Term                This option expires in any event at the close of business at
                    Corporation headquarters on the day before the 8th
                    anniversary of the Date of Grant, as shown in the Notice of
                    Stock Option Grant. (It may expire earlier if your Service
                    terminates, as described above.)

Regular             If your Service terminates for any reason except death,
Termination         Misconduct or Permanent Disability, then this option will
                    expire at the close of business at Corporation headquarters
                    on the date three (3) months after your termination date.
                    The Corporation determines when your Service terminates for
                    this purpose.

Death               If you die while this option is outstanding, then this
                    option will expire at the close of business at Corporation
                    headquarters on the date 12 months after the date of death.

Disability          If your Service terminates because of your Permanent
                    Disability, then this option will expire at the close of
                    business at Corporation headquarters on the date 12 months
                    after your termination date.

                    For all purposes under this Agreement, "Permanent
                    Disability" means that you are unable to engage in any
                    substantial gainful activity by reason of any medically
                    determinable physical or mental impairment which can be
                    expected to result in death or which has lasted, or can be
                    expected to last, for a continuous period of not less than
                    one year.

Leaves of Absence   For purposes of this option, your Service does not terminate
and Part-Time       when you go on a military leave, a sick leave or another
Work                bona fide leave of absence, if the leave was approved by the
                    Corporation in writing. Your Service terminates when the
                    approved leave ends, unless you immediately return to active
                    work.

                    If you go on a leave of absence that lasts or is expected to
                    last seven days or longer, then this option shall not become
                    exercisable for any additional shares and vesting will be
                    suspended during the leave to the extent provided for in the
                    Corporation's leave policy. Upon your return to active work,
                    vesting will resume; however, unless otherwise provided in
                    the Corporation's leave policy, you will not receive credit
                    for any vesting during the period of your leave.

                    If you and the Corporation agree to a reduction in your
                    scheduled work hours, then the Corporation reserves the
                    right to modify the rate at which this option becomes
                    exercisable or vests, so that the rate of vesting is
                    commensurate with your reduced work schedule. Any such
                    adjustment shall be consistent with the Corporation's
                    policies for part-time or reduced work schedules or shall be
                    pursuant to the terms of an agreement between you and the
                    Corporation pertaining to your reduced work schedule.

                                       4

<PAGE>

Misconduct          If your Service terminates for Misconduct, then this option
                    will terminate immediately and cease to be outstanding.
                    "Misconduct" includes fraud, embezzlement, dishonesty or any
                    unauthorized use or disclosure of confidential information
                    or trade secrets of the Corporation or any parent or
                    subsidiary or any other intentional misconduct adversely
                    affecting the business or affairs of the Corporation or a
                    parent or subsidiary of the Corporation.

Restrictions        on Exercise The Corporation will not permit you to exercise
                    this option if the issuance of shares at that time would
                    violate any law, regulation or corporate policy.

Notice of Exercise  When you wish to exercise this option, you must notify the
                    Corporation by filing the proper "Notice of Exercise" form
                    at the address given on the form. Your notice must specify
                    how many shares you wish to purchase. Your notice must also
                    specify how your shares should be registered. The notice
                    will be effective when the Corporation receives it.

                    If someone else wants to exercise this option after your
                    death, that person must prove to the Corporation's
                    satisfaction that he or she is entitled to do so.
                    Furthermore, in no event shall the Corporation's request for
                    satisfactory documentation in connection with an option
                    exercise extend the option's expiration date beyond the time
                    period specified in the above section entitled "Death."

Form of Payment     When you submit your notice of exercise, you must include
                    payment of the option exercise price for the shares that you
                    are purchasing. To the extent permitted by applicable law,
                    payment may be made in one (or a combination of two or more)
                    of the following forms:

                    o    Your personal check, a cashier's check or a money
                         order.

                    o    Certificates for shares of Corporation stock that you
                         own, along with any forms needed to effect a transfer
                         of those shares to the Corporation. The value of the
                         shares, determined as of the effective date of the
                         option exercise, will be applied to the option exercise
                         price. Instead of surrendering shares of Corporation
                         stock, you may attest to the ownership of those shares
                         on a form provided by the Corporation and have the same
                         number of shares subtracted from the option shares
                         issued to you. However, you may not surrender, or
                         attest to the ownership of, shares of Corporation stock
                         in payment of the exercise price if your action would
                         cause the Corporation to recognize compensation expense
                         (or additional compensation expense) with respect to
                         this option for financial reporting purposes.

                                       5

<PAGE>

                    o    Irrevocable directions to a securities broker approved
                         by the Corporation to sell all or part of your option
                         shares and to deliver to the Corporation from the sale
                         proceeds an amount sufficient to pay the option
                         exercise price and any withholding taxes. (The balance
                         of the sale proceeds, if any, will be delivered to
                         you.) The directions must be given by signing a special
                         "Notice of Exercise" form provided by the Corporation.
                         However, payment pursuant to this procedure shall not
                         be permitted if such payment would violate applicable
                         law or a policy of the Corporation.

                    o    Irrevocable directions to a securities broker or lender
                         approved by the Corporation to pledge option shares as
                         security for a loan and to deliver to the Corporation
                         from the loan proceeds an amount sufficient to pay the
                         option exercise price and any withholding taxes. The
                         directions must be given by signing a special "Notice
                         of Exercise" form provided by the Corporation. However,
                         payment pursuant to this procedure shall not be
                         permitted if such payment would violate applicable law
                         or a policy of the Corporation.

Withholding         You will not be allowed to exercise this option unless you
Taxes and Stock     make arrangements acceptable to the Corporation to pay any
Withholding         withholding taxes that may be due as a result of the option
                    exercise. With the Corporation's consent, these arrangements
                    may include withholding shares of Corporation stock that
                    otherwise would be issued to you when you exercise this
                    option. The value of these shares, determined as of the
                    effective date of the option exercise, will be applied to
                    the withholding taxes.

Restrictions        You agree not to sell any option shares at a time when
on Resale           applicable laws, regulations, Corporation trading policies
                    (including the Corporation's Insider Trading Policy, a copy
                    of which can be found on the Corporation's intranet) or an
                    agreement between the Corporation and its underwriters
                    prohibit a sale. This restriction will apply as long as your
                    Service continues and for such period of time after the
                    termination of your Service as the Corporation may specify.

Transfer            In general, only you may exercise this option prior to your
of Option           death. You may not transfer or assign this option, except as
                    provided below. For instance, you may not sell this option
                    or use it as security for a loan. If you attempt to do any
                    of these things, this option will immediate1ly become
                    invalid. You may, however, dispose of this option in your
                    will or in a beneficiary designation.

                                       6

<PAGE>

                    Regardless of any marital property settlement agreement, the
                    Corporation is not obligated to honor a notice of exercise
                    from your former spouse, nor is the Corporation obligated to
                    recognize your former spouse's interest in your option in
                    any other way.

                    If another person wants to exercise this option after it has
                    been transferred to him or her, including a transfer upon
                    your death, that person must prove to the Corporation's
                    satisfaction that he or she is entitled to exercise this
                    option. That person must also complete the proper "Notice of
                    Exercise" form (as described above) and pay the exercise
                    price (as described below).

Retention Rights    Your option or this Agreement does not give you the right to
                    be retained by the Corporation or a subsidiary of the
                    Corporation in any capacity. The Corporation and its
                    subsidiaries reserve the right to terminate your Service at
                    any time, with or without cause.

Stockholder         You, or your estate or heirs, have no rights as a
Rights              stockholder of the Corporation until you have exercised this
                    option by giving the required notice to the Corporation and
                    paying the exercise price. No adjustments are made for
                    dividends or other rights if the applicable record date
                    occurs before you exercise this option.

Adjustments         In the event of a stock split, a stock dividend or a similar
                    change in Common Stock, the number of shares covered by this
                    option and the exercise price per share may be adjusted
                    pursuant to the terms and conditions specified in Section
                    11.1 of the Corporation's 1999 Equity Incentive Plan.

Applicable Law      This Agreement will be interpreted and enforced with respect
                    to issues of contract law under the laws of the State of
                    Texas and with respect to issues of corporation law under
                    the laws of the State of Delaware.

Other Agreements    This Agreement constitutes the entire understanding between
                    you and the Corporation regarding this option. Any prior
                    agreements, commitments or negotiations concerning this
                    option are superseded. This Agreement may be amended only by
                    another written agreement, signed by both parties.

        BY SIGNING THE COVER SHEET OF THIS AGREEMENT, YOU AGREE TO ALL OF
                   THE TERMS AND CONDITIONS DESCRIBED ABOVE.

                                       7