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                                                                   EXHIBIT 10.4

                           ART TECHNOLOGY GROUP, INC.

                   AMENDED AND RESTATED 1996 STOCK OPTION PLAN

1. Purpose

      The purpose of this Amended and Restated 1996 Stock Option Plan (the
"Plan") of Art Technology Group, Inc., a Delaware corporation (the "Company"),
is to advance the interests of the Company's stockholders by enhancing the
Company's ability to attract, retain and motivate persons who are expected to
make important contributions to the Company and by providing such persons with
equity ownership opportunities and performance-based incentives that are
intended to better align their interests with those of the Company's
stockholders. Except where the context otherwise requires, the term "Company"
shall include any of the Company's present or future parent or subsidiary
corporations as defined in Section 424(e) or (f) of the Internal Revenue Code of
1986, as amended, and any regulations promulgated thereunder (the "Code") and
any other business venture (including any joint venture or limited liability
company) in which the Company has a controlling interest, as determined by the
Board of Directors of the Company (the "Board").

2. Eligibility

      All of the Company's employees, officers, directors, consultants and
advisors are eligible to receive options, stock appreciation rights, restricted
stock and other stock-based awards (each, an "Award") under the Plan. Each
person who receives an Award under the Plan is deemed a "Participant".

3. Administration and Delegation

      (a) Administration by Board. The Plan will be administered by the Board.
The Board shall have authority to grant Awards and to adopt, amend and repeal
such administrative rules, guidelines and practices relating to the Plan as it
shall deem advisable. The Board may correct any defect, supply any omission or
reconcile any inconsistency in the Plan or any Award in the manner and to the
extent it shall deem expedient to carry the Plan into effect (including the
interpretation and implementation of Section 11(g)) and it shall be the sole and
final judge of such expediency. All decisions by the Board shall be made in the
Board's sole discretion and shall be final and binding on all persons having or
claiming any interest in the Plan or in any Award. No director or person acting
pursuant to the authority delegated by the Board shall be liable for any action
or determination relating to or under the Plan made in good faith.

      (b) Appointment of Committees. To the extent permitted by applicable law,
the Board may delegate any or all of its powers under the Plan to one or more
committees or subcommittees of the Board (a "Committee"). All references in the
Plan to the "Board" shall mean the Board or a Committee of the Board or the
officers referred to in Section 3(c) to the extent that the Board's powers or
authority under the Plan have been delegated to such Committee or officers.

      (c) Delegation to Officers. To the extent permitted by applicable law, the
Board may delegate to one or more officers of the Company the power to grant
Awards to employees or officers of the Company or any of its present or future
subsidiary corporations and to exercise such other powers under the Plan as the
Board may determine, provided that the Board shall fix the terms of the Awards
to be granted by such officers (including the exercise price of such Awards,
which may include a formula by which the exercise price will be determined) and
the maximum number of shares subject to Awards that the officers may grant;
provided further that no officer shall be authorized to grant Awards to any
"executive officer" of the Company (as defined by Rule 3b-7 under the Securities
Exchange

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Act of 1934, as amended (the "Exchange Act")) or to any "officer" of
the Company (as defined by Rule 16a-1 under the Exchange Act).

4. Stock Available for Awards

      (a) Number of Shares. Subject to adjustment under Section 9, Awards may be
made under the Plan for up to 25,600,000 shares of common stock, $0.01 par value
per share, of the Company (the "Common Stock"). If any Award expires or is
terminated, surrendered or canceled without having been fully exercised or is
forfeited in whole or in part (including as the result of shares of Common Stock
subject to such Award being repurchased by the Company at the original issuance
price pursuant to a contractual repurchase right) or results in any Common Stock
not being issued, the unused Common Stock covered by such Award shall again be
available for the grant of Awards under the Plan, subject, however, in the case
of Incentive Stock Options (as hereinafter defined), to any limitations under
the Code. Shares issued under the Plan may consist in whole or in part of
authorized but unissued shares or treasury shares.

      (b) Sub-limits.

            (1) Section 162(m) Per-Participant Limit. Subject to adjustment
      under Section 9, the maximum number of shares of Common Stock with respect
      to which Awards may be granted to any Participant under the Plan shall be
      1,000,000 per calendar year. For purposes of the foregoing limit, the
      combination of an Option in tandem with an SAR (each as hereinafter
      defined) shall be treated as a single Award. The per-Participant limit
      described in this Section 4(b) shall be construed and applied consistently
      with Section 162(m) of the Code or any successor provision thereto, and
      the regulations thereunder ("Section 162(m)").

            (2) Limit on Awards other than Options and SARS. The maximum number
      of shares with respect to which Awards other than Options and SARs may be
      granted shall be 2,100,000.

5. Stock Options

      (a) General. The Board may grant options to purchase Common Stock (each,
an "Option") and determine the number of shares of Common Stock to be covered by
each Option, the exercise price of each Option and the conditions and
limitations applicable to the exercise of each Option, including conditions
relating to applicable federal or state securities laws, as it considers
necessary or advisable. An Option that is not intended to be an Incentive Stock
Option (as hereinafter defined) shall be designated a "Nonstatutory Stock
Option".

      (b) Incentive Stock Options. An Option that the Board intends to be an
"incentive stock option" as defined in Section 422 of the Code (an "Incentive
Stock Option") shall only be granted to employees of Art Technology Group, Inc.,
any of Art Technology Group, Inc.'s present or future parent or subsidiary
corporations as defined in Section 424(e) or (f) of the Code, and any other
entities the employees of which are eligible to receive Incentive Stock Options
under the Code, and shall be subject to and shall be construed consistently with
the requirements of Section 422 of the Code. The Company shall have no liability
to a Participant, or any other party, if an Option (or any part thereof) that is
intended to be an Incentive Stock Option is not an Incentive Stock Option or for
any action taken by the Board pursuant to Section 10(f), including the
conversion of an Incentive Stock Option to a Nonstatutory Stock Option.

      (c) Exercise Price. The Board shall establish the exercise price of each
Option and specify such exercise price in the applicable option agreement.

      (d) Duration of Options. Each Option shall be exercisable at such times
and subject to such terms and conditions as the Board may specify in the
applicable option agreement.

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      (e) Exercise of Options. Options may be exercised by delivery to the
Company of a written notice of exercise signed by the proper person or by any
other form of notice (including electronic notice) approved by the Board
together with payment in full as specified in Section 5(f) for the number of
shares for which the Option is exercised.

      (f) Payment Upon Exercise. Common Stock purchased upon the exercise of an
Option granted under the Plan shall be paid for as follows:

            (1) in cash or by check, payable to the order of the Company;

            (2) except as the Board may otherwise provide in an option
      agreement, by (A) delivery of an irrevocable and unconditional undertaking
      by a creditworthy broker to deliver promptly to the Company sufficient
      funds to pay the exercise price and any required tax withholding or (B)
      delivery by the Participant to the Company of a copy of irrevocable and
      unconditional instructions to a creditworthy broker to deliver promptly to
      the Company cash or a check sufficient to pay the exercise price and any
      required tax withholding;

            (3) when the Common Stock is registered under the Securities
      Exchange Act of 1934 (the "Exchange Act"), by delivery of shares of Common
      Stock owned by the Participant valued at their fair market value as
      determined by (or in a manner approved by) the Board ("Fair Market
      Value"), provided (A) such method of payment is then permitted under
      applicable law, (B) such Common Stock, if acquired directly from the
      Company, was owned by the Participant at least six months prior to such
      delivery and

      (C) such Common Stock is not subject to any repurchase, forfeiture,
      unfulfilled vesting or other similar requirements;

            (4) to the extent permitted by applicable law and by the Board, by
      (A) delivery of a promissory note of the Participant to the Company on
      terms determined by the Board or (B) payment of such other lawful
      consideration as the Board may determine; or

            (5) by any combination of the above permitted forms of payment.

      (g) Substitute Options. In connection with a merger or consolidation of an
entity with the Company or the acquisition by the Company of property or stock
of an entity, the Board may grant Options in substitution for any options or
other stock or stock-based awards granted by such entity or an affiliate
thereof. Substitute Options may be granted on such terms as the Board deems
appropriate in the circumstances, notwithstanding any limitations on Options
contained in the other sections of this Section 5 or in Section 2.

6. Stock Appreciation Rights

      (a) Nature. A Stock Appreciation Right ("SAR") is an Award entitling the
holder on exercise to receive an amount in cash or Common Stock or a combination
thereof (such form to be determined by the Board) determined in whole or in part
by reference to appreciation, from and after the date of grant, in the fair
market value of a share of Common Stock. SARs may be based solely on
appreciation in the fair market value of Common Stock or on a comparison of such
appreciation with some other measure of market growth such as (but not limited
to) appreciation in a recognized market index. The date as of which such
appreciation or other measure is determined shall be the exercise date unless
another date is specified by the Board in the SAR Award.

      (b) Grants. SARs may be granted in tandem with, or independently of,
Options granted under the Plan.

            (1) Tandem Awards. When SARs are expressly granted in tandem with
      Options: (A) the SAR will be exercisable only at such time or times, and
      to the extent, that the related Option is exercisable and will be

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      exercisable in accordance with the procedure required for exercise of the
      related Option; (B) the SAR will terminate and no longer be exercisable
      upon the termination or exercise of the related Option, except that a SAR
      granted with respect to less than the full number of shares covered by an
      Option will not be reduced until the number of shares as to which the
      related Option has been exercised or has terminated exceeds the number of
      shares not covered by the SAR; (C) the Option will terminate and no longer
      be exercisable upon the exercise of the related SAR; and (D) the SAR will
      be transferable only with the related Option.

            (2) Independent SARs. A SAR not expressly granted in tandem with an
      Option will become exercisable at such time or times, and on such
      conditions, as the Board may specify in the SAR Award.

      (c) Exercise. A SAR may be exercised only by delivery to the Company of a
written notice of exercise signed by the proper person or other form of notice
(including electronic notice) approved by the Board, together with any other
documents required by the Board.

7. Restricted Stock.

      (a) Grants. The Board may grant Awards entitling recipients to acquire
shares of Common Stock, subject to the right of the Company to repurchase all or
part of such shares at their issue price or other stated or formula price (or to
require forfeiture of such shares if issued at no cost) from the recipient in
the event that conditions specified by the Board in the applicable Award are not
satisfied prior to the end of the applicable restriction period or periods
established by the Board for such Award (each, a "Restricted Stock Award").

      (b) Terms and Conditions. The Board shall determine the terms and
conditions of a Restricted Stock Award, including the conditions for repurchase
(or forfeiture) and the issue price, if any.

      (c) Stock Certificates. Any stock certificates issued in respect of a
Restricted Stock Award shall be registered in the name of the Participant and,
unless otherwise determined by the Board, deposited by the Participant, together
with a stock power endorsed in blank, with the Company (or its designee). At the
expiration of the applicable restriction periods, the Company (or such designee)
shall deliver the certificates no longer subject to such restrictions to the
Participant or the Designated Beneficiary of such Participant. For these
purposes, a "Designated Beneficiary" of a Participant shall be (1) a beneficiary
designated by such Participant, in a manner determined by the Board, to receive
amounts due or exercise rights of such Participant in the event of such
Participant's death or (2) in the absence of such a designation, the
Participant's estate.

      (d) Deferred Delivery of Shares. The Board may, at the time any Restricted
Stock Award is granted, provide that, at the time Common Stock would otherwise
be delivered pursuant to the Award, the Participant shall instead receive an
instrument evidencing the right to future delivery of Common Stock at such time
or times, and on such conditions, as the Board shall specify. The Board may at
any time accelerate the time at which delivery of all or any part of the Common
Stock shall take place.

8. Other Stock-Based Awards

      Other Awards of shares of Common Stock, and other Awards that are valued
in whole or in part by reference to, or are otherwise based on, shares of Common
Stock or other property, may be granted under the Plan to Participants ("Other
Stock Unit Awards"), including Awards entitling recipients to receive shares of
Common Stock to be delivered in the future. Such Other Stock Unit Awards shall
also be available as a form of payment in the settlement of other Awards granted
under the Plan or as payment in lieu of compensation to which a Participant is
otherwise entitled. Other Stock Unit Awards may be paid in shares of Common
Stock or cash, as the Board shall determine. Subject to the provisions of the
Plan, the Board shall determine the conditions of each Other Stock Unit Awards,
including any purchase price applicable thereto. At the time any Award is
granted, the Board may provide that, at the time Common Stock would otherwise be
delivered pursuant to the Award, the Participant will instead receive an
instrument evidencing the Participant's right to future delivery of the Common
Stock.

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9. Adjustments for Changes in Common Stock and Certain Other Events

      (a) Changes in Capitalization. In the event of any stock split, reverse
stock split, stock dividend, recapitalization, combination of shares,
reclassification of shares, spin-off or other similar change in capitalization
or event, or any distribution to holders of Common Stock other than an ordinary
cash dividend, (1) the number and class of securities available under the Plan,
(2) sub-limits set forth in Section 4(b), (3) the number and class of securities
and exercise price per share of each outstanding Option, (4) the repurchase
price per share subject to each outstanding Restricted Stock Award and (5) the
share- and per-share-related provisions of each outstanding SAR and Other Stock
Unit Award, shall be appropriately adjusted by the Company (or substituted
Awards may be made, if applicable) to the extent determined by the Board.

      (b) Reorganization Events.

            (1) Definition. A "Reorganization Event" shall mean: (A) any merger
      or consolidation of the Company with or into another entity as a result of
      which all of the Common Stock of the Company is converted into or
      exchanged for the right to receive cash, securities or other property, (B)
      any exchange of all of the Common Stock of the Company for cash,
      securities or other property pursuant to a share exchange transaction or
      (C) any liquidation or dissolution of the Company.

            (2) Consequences of a Reorganization Event on Awards Other than
      Restricted Stock Awards. In connection with a Reorganization Event, the
      Board shall have the authority to take, in its discretion, any of the
      following actions as to all or any outstanding Awards on such terms as the
      Board determines:

                  (A) provide that Awards shall be assumed, or substantially
            equivalent Awards shall be substituted, by the acquiring or
            succeeding corporation (or an affiliate thereof),

                  (B) upon written notice to a Participant, provide that the
            Participant's unexercised Options or other unexercised Awards shall
            become exercisable in full and will terminate immediately prior to
            the consummation of such Reorganization Event unless exercised by
            the Participant within a specified period following the date of such
            notice,

                  (C) provide that outstanding Awards shall become realizable or
            deliverable, or restrictions applicable to an Award shall lapse, in
            whole or in part prior to or upon such Reorganization Event,

                  (D) in the event of a Reorganization Event under the terms of
            which holders of Common Stock will receive upon consummation thereof
            a cash payment for each share surrendered in the Reorganization
            Event (the "Acquisition Price"), make or provide for a cash payment
            to a Participant equal to (i) the Acquisition Price times the number
            of shares of Common Stock subject to the Participant's Options or
            other Awards (to the extent the exercise price does not exceed the
            Acquisition Price) minus (ii) the aggregate exercise price of all
            such outstanding Options or other Awards, in exchange for the
            termination of such Options or other Awards,

                  (E) provide that, in connection with a liquidation or
            dissolution of the Company, Awards shall convert into the right to
            receive liquidation proceeds (if applicable, net of the exercise
            price thereof), and

                  (F) any combination of the foregoing.

      For purposes of clause (A) above, an Option shall be considered assumed
if, following consummation of the Reorganization Event, the Option confers the
right to purchase, for each share of Common Stock subject to the Option
immediately prior to the consummation of the Reorganization Event, the
consideration (whether cash,

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securities or other property) received as a result of the Reorganization Event
by holders of Common Stock for each share of Common Stock held immediately prior
to the consummation of the Reorganization Event (and if holders were offered a
choice of consideration, the type of consideration chosen by the holders of a
majority of the outstanding shares of Common Stock); provided that if the
consideration received as a result of the Reorganization Event is not solely
common stock of the acquiring or succeeding corporation (or an affiliate
thereof), the Company may, with the consent of the acquiring or succeeding
corporation, provide for the consideration to be received upon the exercise of
Options to consist solely of common stock of the acquiring or succeeding
corporation (or an affiliate thereof) equivalent in fair market value to the per
share consideration received by holders of outstanding shares of Common Stock as
a result of the Reorganization Event.

      To the extent all or any portion of an Option becomes exercisable solely
as a result of clause (B) above, the Board may provide that upon exercise of
such Option the Participant shall receive shares subject to a right of
repurchase by the Company or its successor at the Option exercise price; such
repurchase right (i) shall lapse at the same rate as the Option would have
become exercisable under its terms and (ii) shall not apply to any shares
subject to the Option that were exercisable under its terms without regard to
clause (B) above.

            (3) Consequences of a Reorganization Event on Restricted Stock
      Awards. Upon the occurrence of a Reorganization Event other than a
      liquidation or dissolution of the Company, the repurchase and other rights
      of the Company under each outstanding Restricted Stock Award shall inure
      to the benefit of the Company's successor and shall apply to the cash,
      securities or other property that the Common Stock was converted into or
      exchanged for pursuant to such Reorganization Event in the same manner and
      to the same extent as they applied to the Common Stock subject to such
      Restricted Stock Award. Upon the occurrence of a Reorganization Event
      involving the liquidation or dissolution of the Company, except to the
      extent specifically provided to the contrary in the instrument evidencing
      any Restricted Stock Award or any other agreement between a Participant
      and the Company, all restrictions and conditions on all Restricted Stock
      Awards then outstanding shall automatically be deemed terminated or
      satisfied.

10. General Provisions Applicable to Awards

      (a) Transferability of Awards. Except as the Board may otherwise determine
or provide in an Award, Awards shall not be sold, assigned, transferred, pledged
or otherwise encumbered by the person to whom they are granted, either
voluntarily or by operation of law, except by will or the laws of descent and
distribution or, other than in the case of an Incentive Stock Option, pursuant
to a qualified domestic relations order, and, during the life of the
Participant, shall be exercisable only by the Participant. References to a
Participant, to the extent relevant in the context, shall include references to
authorized transferees.

      (b) Documentation. Each Award shall be evidenced in such form (written,
electronic or otherwise) as the Board shall determine. Each Award may contain
terms and conditions in addition to those set forth in the Plan.

      (c) Board Discretion. Except as otherwise provided by the Plan, each Award
may be made alone or in addition or in relation to any other Award. The terms of
each Award need not be identical, and the Board need not treat Participants
uniformly.

      (d) Termination of Status. The Board shall determine the effect on an
Award of the disability, death, retirement, authorized leave of absence or other
change in the employment or other status of a Participant and the extent to
which, and the period during which, the Participant, or the Participant's legal
representative, conservator, guardian or Designated Beneficiary, may exercise
rights under the Award.

      (e) Withholding. Each Participant shall pay to the Company, or make
provision satisfactory to the Company for payment of, any taxes required by law
to be withheld in connection with an Award to such Participant. Except as the
Board may otherwise provide in an Award, for so long as the Common Stock is
registered under the Exchange Act, Participants may satisfy such tax obligations
in whole or in part by delivery of shares of Common Stock, including

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shares retained from the Award creating the tax obligation, valued at their Fair
Market Value; provided that the total tax withholding where stock is being used
to satisfy such tax obligations cannot exceed the Company's minimum statutory
withholding obligations (based on minimum statutory withholding rates for
federal and state tax purposes, including payroll taxes, that are applicable to
such supplemental taxable income). Shares surrendered to satisfy tax withholding
requirements cannot be subject to any repurchase, forfeiture, unfulfilled
vesting or other similar requirements. The Company may, to the extent permitted
by law, deduct any such tax obligations from any payment of any kind otherwise
due to a Participant.

      (f) Amendment of Award. The Board may amend, modify or terminate any
outstanding Award, including substituting therefor another Award of the same or
a different type, changing the date of exercise or realization, and converting
an Incentive Stock Option to a Nonstatutory Stock Option, provided that the
Participant's consent to such action shall be required unless the Board
determines that the action, taking into account any related action, would not
materially and adversely affect the Participant.

      (g) Conditions on Delivery of Stock. The Company will not be obligated to
deliver any shares of Common Stock pursuant to the Plan or to remove
restrictions from shares previously delivered under the Plan until (1) all
conditions of the Award have been met or removed to the satisfaction of the
Company, (2) in the opinion of the Company's counsel, all other legal matters in
connection with the issuance and delivery of such shares have been satisfied,
including any applicable securities laws and any applicable stock exchange or
stock market rules and regulations, and (3) the Participant has executed and
delivered to the Company such representations or agreements as the Company may
consider appropriate to satisfy the requirements of any applicable laws, rules
or regulations.

      (h) Acceleration. The Board may at any time provide that any Award shall
become immediately exercisable in full or in part, free of some or all
restrictions or conditions, or otherwise realizable in full or in part, as the
case may be.

      (i) Performance Conditions.

            (1) This Section 10(i) shall be administered by a Committee approved
      by the Board, all of the members of which are "outside directors" as
      defined by Section 162(m) (the "Section 162(m) Committee").

            (2) Notwithstanding any other provision of the Plan, if the Section
      162(m) Committee determines at the time a Restricted Stock Award or Other
      Stock Unit Award is granted to a Participant who is then an officer, that
      such Participant is, or is likely to be as of the end of the tax year in
      which the Company would claim a tax deduction in connection with such
      Award, a Covered Employee (as defined in Section 162(m)), then the Section
      162(m) Committee may provide that this Section 10(i) is applicable to such
      Award.

            (3) If a Restricted Stock Award or Other Stock Unit Award is subject
      to this Section 10(i), than the lapsing of restrictions thereon and the
      distribution of cash or Shares pursuant thereto, as applicable, shall be
      subject to the achievement of one or more objective performance goals
      established by the Section 162(m) Committee, which:

                  (A) shall be set by the Section 162(m) Committee within the
            time period prescribed by, and shall otherwise comply with the
            requirements of, Section 162(m);

                  (B) shall be based on the attainment of specified levels of
            one or any combination of the following: (i) earnings per share;
            (ii) return on average equity or average assets with respect to a
            pre-determined peer group; (iii) earnings; (iv) earnings growth; (v)
            revenues; (vi) expenses; (vii) stock price; (viii) market share;
            (ix) return on sales, assets, equity or investment; (x) regulatory
            compliance; (xi) improvement of financial ratings; (xii) achievement
            of balance sheet or income statement objectives; (xiii) total
            shareholder return; (xiv) net operating profit after tax; (xv)
            pre-tax or after-tax income; (xvi) cash flow; or (xvii) such other

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            objective goals as are established by the Board;

                  (C) may be absolute in their terms or measured against or in
            relationship to other companies comparably, similarly or otherwise
            situated;

                  (D) may be adjusted to exclude any one or more of (i)
            extraordinary items, (ii) gains or losses on the dispositions of
            discontinued operations, (iii) the cumulative effects of changes in
            accounting principles, (iv) the writedown of any asset and (v)
            charges for restructuring and rationalization programs; and

                  (E) may vary by Participant and may be different for different
            Awards.

            (4) Notwithstanding any provision of the Plan, with respect to any
      Restricted Stock Award or Other Stock Unit Award that is subject to this
      Section 10(i), the Section 162(m) Committee:

                  (A) may adjust downwards, but not upwards, the cash or number
            of Shares payable pursuant to such Award; and

                  (B) may not waive the achievement of the applicable
            performance goals except in the case of the death or disability of
            the Participant.

            (5) The Section 162(m) Committee shall have the power to impose such
      other restrictions on Awards subject to this Section 10(i) as it may deem
      necessary or appropriate to ensure that such Awards satisfy all
      requirements for "performance-based compensation" within the meaning of
      Section 162(m)(4)(C) of the Code, or any successor provision thereto.

11. Miscellaneous

      (a) No Right To Employment or Other Status. No person shall have any claim
or right to be granted an Award, and the grant of an Award shall not be
construed as giving a Participant the right to continued employment or any other
relationship with the Company. The Company expressly reserves the right at any
time to dismiss or otherwise terminate its relationship with a Participant free
from any liability or claim under the Plan, except as expressly provided in the
applicable Award.

      (b) No Rights As Stockholder. Subject to the provisions of the applicable
Award, no Participant or Designated Beneficiary shall have any rights as a
stockholder with respect to any shares of Common Stock to be distributed with
respect to an Award until becoming the record holder of such shares.
Notwithstanding the foregoing, in the event the Company effects a split of the
Common Stock by means of a stock dividend and the exercise price of and the
number of shares subject to such Option are adjusted as of the date of the
distribution of the dividend (rather than as of the record date for such
dividend), then an optionee who exercises an Option between the record date and
the distribution date for such stock dividend shall be entitled to receive, on
the distribution date, the stock dividend with respect to the shares of Common
Stock acquired upon such Option exercise, notwithstanding the fact that such
shares were not outstanding as of the close of business on the record date for
such stock dividend.

      (c) Effective Date and Term of Plan. The Plan shall become effective on
the date on which it is adopted by the Board, but no Award may be granted unless
and until the Plan has been approved by the Company's stockholders. No Awards
shall be granted under the Plan after December 31, 2013, but Awards previously
granted may extend beyond that date.

      (d) Amendment of Plan. The Board may amend, suspend or terminate the Plan
or any portion thereof at any time, provided that, to the extent determined by
the Board, no amendment requiring stockholder approval under any

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applicable legal, regulatory or listing requirement shall become effective until
such stockholder approval is obtained. No Award shall be made that is
conditioned upon stockholder approval of any amendment to the Plan.

      (e) Provisions for Foreign Participants. The Board may modify Awards or
Options granted to Participants who are foreign nationals or employed outside
the United States or establish subplans or procedures under the Plan to
recognize differences in laws, rules, regulations or customs of such foreign
jurisdictions with respect to tax, securities, currency, employee benefit or
other matters.

      (f) Governing Law. The provisions of the Plan and all Awards made
hereunder shall be governed by and interpreted in accordance with the laws of
the State of Delaware, without regard to any applicable conflicts of law.

      (g) Effect of Restatement. This Amendment and Restatement of the Plan
shall not be effective until approved by the stockholders of the Company. All
Awards to Participants outstanding as of the date of the Amendment and
Restatement of the Plan shall continue in full force and effect without
modification by such Amendment and Restatement; provided that each reference in
any such Awards to a section of the Plan as in effect prior to the restatement
shall be deemed to refer to the corresponding section of the Plan as restated
unless the reference to such corresponding section would have an adverse impact
on the Participant holding the applicable Award.

      (h) Construction. The headings of the Sections of the Plan are included
only for convenience and shall not affect the meaning or interpretation of the
Plan. Except as otherwise expressly provided, references herein to Sections
shall mean such Sections of the Plan. The word "including" as used in the Plan
shall not be construed so as to exclude any other thing not referred to or
described.

                                 AMENDMENT NO. 5
                        TO THE 1996 STOCK OPTION PLAN OF
                           ART TECHNOLOGY GROUP, INC.

      Pursuant to Section 19 of the 1996 Stock Option Plan (the "Plan") of Art
Technology Group, Inc. (the "Company"), the Plan is hereby amended as follows:

      1. Resolved: Section 6(b)(ii) be and hereby is amended by deleting the
first parenthetical under such section.

                                Approved by the Board of Directors
                                February 3, 2005

                                      -9-<PAGE>
                                                                    EXHIBIT 10.1

          CONFIDENTIAL MATERIALS OMITTED AND FILED SEPARATELY WITH THE
         SECURITIES AND EXCHANGE COMMISSION. ASTERISKS DENOTE OMISSIONS.

                                    AGREEMENT

This agreement is made by and between

IDENIX PHARMACEUTICALS, INC., a corporation organized and existing under the
laws of the State of Delaware, having its principal offices located at 60
Hampshire Street, Cambridge, MA 02139 represented by its legal representative
Mr. Jean-Pierre Sommadossi (hereinafter referred to as "Idenix")

                                       and

IDENIX SARL, a corporation organized and existing under the laws of France,
having registered offices in Immueuble "La Vigie" 170 rue Leon Blum, 34000
Montpellier, France, represented by its legal representative Mr. Jean-Marc
Allaire (hereinafter referred to as "Idenix SARL")

                                       and

UNIVERSITA' DEGLI STUDI DI CAGLIARI, having a principal place of business at
Cittadella Universitaria, SS 554 KM 4.5, 09133 Monserrato, Cagliari, Italy,
represented by the Chancellor Prof. Pasquale Mistretta (hereinafter referred to
as the "University")

                                     whereas

a) on 4 January 1999, the University and Idenix SARL, this last on behalf and
for the benefit of Idenix, entered into an agreement entitled "Co-operative
Antiviral Research Activity Agreement" (hereinafter referred to as the
"Co-operative Agreement") aimed at performing a joint research activity in the
antiviral substances field;

b) in accordance with the Co-operative Agreement, on 14 December 2000, the
University and Idenix entered into a license agreement (hereinafter the "License
Agreement") according to which the University grants to Idenix the exclusive
license for the exploitation, whether direct or indirect, of the results
obtained and that will be obtained from the performance of the activity
indicated under the previous point;

c) the above mentioned Co-operative Agreement and License Agreement (together,
the "Original Agreements") have been initially amended on 10 April 2002;

d) the Original Agreements, as so amended, have been afterwards amended with the
deed undersigned by the parties on 8 May 2003, also in consideration of the
transactions at that time pending between Idenix and Novartis Pharma AG for the

<PAGE>

acquisition, by this last, of the majority of the shareholding of Idenix (the
amendments indicated in this point have become effective on 8 May 2003,
following to the occurred execution of a "Development, License and
Commercialization Agreement" and of a "Manufacturing and Supply Agreement" by
and among Idenix, Idenix (Cayman) Limited and Novartis) (together, the "Novartis
Agreements");

e) the parties further amended the Original Agreements, as previously amended,
on 30 June 2004 (the "June 30 Letter Amendment");

f) with the present agreement the parties intend to further amend the terms of
the Original Agreements (the "Original Agreements", as amended through and
including this agreement, collectively, the "Cagliari Agreements", provided that
the "Cagliari Agreements" do not include the "Novartis Agreements");

now, therefore, in consideration of the premises and the mutual covenants herein
contained, Idenix, Idenix SARL and the University agree as follows:

1. The premises shall represent an integral and substantial part of this
agreement. Capital letter terms used and not otherwise defined herein shall
refer to the definitions provided under the Cagliari Agreements, which shall
apply for the purposes of this agreement.

2. "Subject Intellectual Property Rights" shall mean (A) those families of
patents and families of patent applications (including U.S. provisional patent
applications, conversions, continuations, divisions, continuations-in-part
thereof) (i) whose earliest priority filing date is before May 14, 2003 or (ii)
which include compounds or methods first disclosed in a patent or patent
application whose earliest priority filing date is before May 14, 2003, and
which are set forth in Exhibit A attached hereto under the caption "Original
Patents" ("Original Patents"); and (B) those families of patents and families of
patent applications (including U.S. provisional patent applications,
conversions, continuations, divisions and continuations-in-part thereof) other
than Original Patents whose earliest priority filing date is on or after 14 May
2003, and which are set forth in Exhibit A attached hereto under the caption
"Subsequent Patents" ("Subsequent Patents"). Exhibit A attached hereto shall
also replace and supercede the current Annex A to the License Agreement.
Subsequent amendments to Exhibit A shall occur as contemplated in paragraph five
of the June 30 Letter Amendment.

3. "Valid Claim" shall mean a claim (a) of any issued, unexpired patent included
in the Subject Intellectual Property Rights that has not been revoked or held
unenforceable or invalid by a decision of a court or governmental agency of
competent jurisdiction from which no appeal can be taken, or with respect to
which an appeal is not taken within the time allowed for appeal, and that has
not been disclaimed or admitted to be invalid or unenforceable through reissue,
disclaimer or otherwise, or (b) of any patent application included in the
Subject Intellectual Property Rights that has not been cancelled, withdrawn or
abandoned or been pending for more than ten (10) years.

4. The parties hereby agree that, in connection with any Subject Intellectual
Property Right sublicensed by Idenix to an Affiliate, Idenix shall pay to the
University:

                                        2

<PAGE>

          A.   a royalty rate amounting to:

                    (i)  [**]% of Net Sales performed, after the Effective Date
                         as defined under article 6, by such Affiliate (or its
                         Affiliates and/or sublicensees) of products which, but
                         for the license granted under the Cagliari Agreements,
                         would infringe one or more Valid Claims of an Original
                         Patent;

                    and

                    (ii) [**]% of Net Sales performed, after the Effective Date
                         as defined under article 6, by such Affiliate (or its
                         Affiliates and/or sublicensees) of products which, but
                         for the license granted under the Cagliari Agreements,
                         would infringe one or more Valid Claims of a Subsequent
                         Patent only;

     plus

          B.   a percentage of any license fee, milestone payment and other cash
               consideration, paid to Idenix by such Affiliate after the
               Effective Date as defined under article 6 (excluding royalties
               and amounts paid to fund or reimburse research, development,
               manufacturing or commercialization expenses) with respect to
               research, development or commercialization of products which, but
               for the license granted under the Cagliari Agreements, the sale
               of which products would infringe one or more Valid Claims of any
               Subject Intellectual Property Right (an "Affiliate Fee"),
               amounting to:

                    (i)  [**]% of any Affiliate Fee where a relevant Subject
                         Intellectual Property Right is an Original Patent;

                    and

                    (ii) [**]% of any Affiliate Fee where the relevant Subject
                         Intellectual Property Right consists only of one or
                         more Subsequent Patents.

For clarification, in no event shall the University have any right or claim to
payments made by an Affiliate with respect to an Affiliate's purchase of Idenix
securities, any Idenix financing or any other payment made by an Affiliate other
than such payments which specifically relate to the Subject Intellectual
Property Rights and drug products covered thereby, as provided above. The
parties hereby agree that Novartis is an Affiliate.

In the case of direct exploitation by Idenix and / or of licensing to a third
party other than an Affiliate, the terms of the License Agreement as in effect
immediately prior to this agreement are and remain in effect unmodified by this
agreement.

                                        3

<PAGE>

5. As regards the method of payment of the amounts indicated in the foregoing
art. 4 of this agreement, the parties hereby agree that art. 4 of the License
Agreement shall apply.

6. The amendments provided under the present agreement shall apply from the date
of its subscription by the last of all the subscribing parties to so subscribe
(the "Effective Date").

7. Notwithstanding anything in the Cagliari Agreements, Idenix and Idenix SARL
or their successor(s) shall have the right, without the University's consent, to
amend, modify or terminate any agreements, including the Novartis Agreements,
but excluding the Cagliari Agreements.

8. This agreement is drafted in English and, for the sole purpose of allowing
the University to better comprehend the relevant content, in Italian, being
understood that in case of contrasts between the English version and the Italian
version, the English one shall prevail.

9. Except as amended hereby, the Original Agreements remain in full force and
effect.

                  [Remainder of Page Intentionally Left Blank]

                                       4

<PAGE>

IN WITNESS WHEREOF, Idenix, Idenix SARL and the University have caused this
agreement to be duly executed by their authorized representatives.

IDENIX PHARMACEUTICALS, INC.

By: /s/ Andrea J. Corcoran
    ---------------------------------
Name: Andrea J. Corcoran
Title: Executive Vice President,
       Legal and Administration

Date October 24, 2005

IDENIX SARL

By: /s/ Jean-Pierre Sommadossi
    ---------------------------------
Name: Jean-Pierre Sommadossi
Title: Chairman and Chief Executive
       Officer

Date October 24, 2005

THE UNIVERSITY

By: /s/ Pasquale Mistretta
    ---------------------------------
    Prof. Pasquale Mistretta
    Chancellor of the University

Date October 24, 2005

By: /s/ Paolo La Colla
    ---------------------------------
    Prof. Paolo La Colla

Date October 24, 2005

<PAGE>

                                    EXHIBIT A

<TABLE>
<CAPTION>
                                                      ORIGINAL PATENTS
------------------------------------------------------------------------------------------------------------------------------------
                                                                                                  PATENT /     ISSUE /
                                                                         FILING      SERIAL      PUBLICATION    PUB.
      TITLE & DOCKET NAME            COUNTRY      OWNER    INVENTORS      DATE       NUMBER        NUMBER       DATE       STATUS
-------------------------------  --------------  ------  -------------  --------  ------------  -----------   --------  ------------
<S>                              <C>             <C>     <C>            <C>       <C>           <C>           <C>       <C>
[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

IDX 1006                         U.S.              USC   P. LaColla,    5/26/01   09/863,816    2003/0060400  3/27/03   Allowed
                                                 IDXINC  JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

IDX 1006 CON 3                   U.S.              USC   P. LaColla,    6/20/03   10/602,692    2004/0097462  5/20/04   Published
                                                 IDXINC  JP Sommadossi

IDX 1006 DIV                     U.S.              USC   P. LaColla,    6/20/03   10/602,693    2004/0063622  4/01/04   Published
                                                 IDXINC  JP Sommadossi

IDX 1006                         PCT               USC   P. LaColla,    5/26/01   US01/16687    WO 01/92282   12/06/01  National
                                                 IDXCAY  JP Sommadossi                                                  Phase
                                                                                                                        Entered

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

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[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

IDX 1006                         Venezuela         USC   P. LaColla,    5/26/01   1134-2001     459                     Published
                                                 IDXCAY  JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

IDX 1006                         Thailand          USC   P. LaColla,    5/26/01   065737        58870                   Published
                                                 IDXCAY  JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]
</TABLE>

<PAGE>

<TABLE>
<S>                              <C>             <C>     <C>            <C>       <C>           <C>           <C>       <C>
IDX 1006                         Brazil            USC   P. LaColla,    5/26/01   200200759     1735                    Published
                                                 IDXCAY  JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

IDX 1006                         China             USC   P. LaColla,    5/26/01   01813182.4    1468249                 Published
                                                 IDXCAY  JP Sommadossi

IDX 1006                         Czech Republic    USC   P. LaColla,    5/26/01   PV 2002-4225  10-2003                 Published
                                                 IDXCAY  JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

IDX 1006                         Hong Kong         USC   P. LaColla,    5/26/01   03102884.2    1051203                 Published
                                                 IDXCAY  JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

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[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

IDX 1007                         U.S.              USC   P. LaColla,    5/23/01   09/864,078    2003/0050229  3/13/03   Allowed
                                                 IDXINC  JP Sommadossi

IDX 1007 CON 1                   U.S.              USC   P. LaColla,    6/20/03   10/602,691    2004/0097461  5/20/04   Published
                                                 IDXINC  JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

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[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]
</TABLE>

<PAGE>

<TABLE>
<S>                              <C>             <C>     <C>            <C>       <C>           <C>           <C>       <C>
[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

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[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

IDX 1007                         Brazil            USC   P. LaColla,    5/23/01   0111127-2     1694                    Published
                                                 IDXCAY  JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

IDX 1007                         China             USC   P. LaColla,    5/23/01   01813233.2    1443191                 Published
                                                 IDXCAY  JP Sommadossi

IDX 1007                         Czech Republic    USC   P. LaColla,    5/23/01   PV2002-4149   9-2003                  Published
                                                 IDXCAY  JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

IDX 1007                         Hong Kong         USC   P. LaColla,    5/23/01   03102883.3    1051202                 Published
                                                 IDXCAY  JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

IDX 1007                         Indonesia         USC   P. LaColla,    5/23/01   W-0020020287  036.654A                Published
                                                 IDXCAY  JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                  [**]

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</TABLE>

<PAGE>

<TABLE>
<S>                              <C>             <C>     <C>            <C>       <C>          <C>           <C>       <C>
[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

IDX 1008                         U.S.              USC   P. LaColla,    4/11/02   10/122,252   6,710,068     3/24/04   Patented
                                                 IDXINC  M. Artico,
                                                         JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

IDX 1008                         PCT               USC   P. LaColla,    4/11/02   US02/11736   WO 02/083126  10/24/02  Published
                                                 IDXCAY  M. Artico,
                                                         JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

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[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

IDX 1008                         Europe            USC   P. LaColla,    4/11/02   20020723853  1390029                 Published
                                                 IDXCAY  M. Artico,
                                                         JP Sommadossi

[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

[**]                             [**]             [**]   [**]           [**]      [**]         [**]          [**]      [**]

                                                   USC   JP Sommadossi  1/24/03   10/350,772   2003/0225114  12/4/03   Published
IDX 1009 CON 1                   U.S. CON        IDXINC  P. LaColla
                                                         M. Artico
                                                         M. Bryant

[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

                                                   USC   JP Sommadossi  11/19/01  US01/45652   WO 02/40021   5/23/02   National
IDX 1009                         PCT             IDXCAY  P. LaColla                                                    Phase
                                                         M. Artico                                                     Entered
                                                         M. Bryant

[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

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[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]
</TABLE>

<PAGE>

<TABLE>
<S>                              <C>             <C>     <C>            <C>       <C>          <C>           <C>       <C>
IDX 1017  2' and 3' -            PCT              CNRS,  G. Gosselin    6/27/03   IB03/03901   WO 04/003000  1/8/04    Published
Nucleoside Prodrugs                                USC   JP Sommadossi
for Treating Hepatitis C Virus                   IDXCAY  P. LaColla
                                                         R. Storer

[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

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</TABLE>

<PAGE>

<TABLE>
<S>                              <C>             <C>     <C>            <C>       <C>          <C>           <C>       <C>
IDX 1020                         PCT               USC   JP Sommadossi  8/7/03    US03/24957   WO 04/014364  2/19/04   Published
                                                 IDXCAY  P. LaColla
                                                         R. Storer
                                                         A. Moussa
                                                         M. Artico
                                                         R. Silvestri

[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

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IDX 1031  2'-C-Methyl-3'- O-     U.S.             USC    JP Sommadossi  6/27/03   10/607,909   2004/0077587  4/22/04   Published
L-Valine Ester Ribofuranosyl                     IDXINC  P. LaColla
Cytidine for Treatment of
Flaviviridae Infections (NM283)

IDX 1031                         PCT              USC    JP Sommadossi  6/25/03   US03/20431   WO 04/002422  1/8/04    Published
                                                 IDXCAY  P. LaColla

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</TABLE>

<PAGE>

<TABLE>
<CAPTION>
                                                      SUBSEQUENT PATENTS
------------------------------------------------------------------------------------------------------------------------------------
                                                                                                 PATENT /    ISSUE /
                                                                         FILING      SERIAL     PUBLICATION    PUB.
      TITLE & DOCKET NAME            COUNTRY      OWNER    INVENTORS      DATE       NUMBER       NUMBER       DATE        STATUS
-------------------------------  --------------  ------  -------------  --------  -----------  ------------  --------  -------------
<S>                              <C>             <C>     <C>            <C>       <C>          <C>           <C>       <C>
[**]                             [**]             [**]   [**]           [**]      [**]                                 [**]

[**]                             [**]             [**]   [**]           [**]      [**]

[**]                             [**]             [**]   [**]           [**]      [**]
</TABLE>

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00093-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00093-of-00352.parquet"}]]