1
                                                                    Exhibit 10.1


                               COSTAR GROUP, INC.
                            1998 STOCK INCENTIVE PLAN
                          (AS AMENDED ON JULY 13, 1999)


PURPOSE        CoStar Group, Inc., a Delaware corporation "CoStar" or the
               "Company"), wishes to recruit, reward, and retain employees and
               outside directors. To further these objectives, the Company
               hereby sets forth the CoStar Group, Inc. 1998 Stock Incentive
               Plan (the "Plan") to provide options ("Options") or direct grants
               ("Stock Grants" and, together with the Options, "Awards") to
               employees and outside directors with respect to shares of the
               Company's common stock (the "Common Stock"). The Plan is
               effective as of the effective date (the "Effective Date") of the
               Company's registration under Section 12 of the Securities
               Exchange Act of 1934 (the "Exchange Act") with respect to its
               initial public offering ("IPO").

PARTICIPANTS   All Employees of CoStar and any Eligible Subsidiaries are
               eligible for Options and Stock Grants under this Plan, as are the
               directors of CoStar and the Eligible Subsidiaries who are not
               employees ("Eligible Directors"). Eligible employees and
               directors become "optionees" when the Administrator grants them
               an option under this Plan or "recipients" when they receive a
               direct grant of Common Stock. (Optionees and recipients are
               referred to collectively as "participants." The term participant
               also includes, where appropriate, a person authorized to exercise
               an Award in place of the original optionee.) The Administrator
               may also grant Options or make Stock Grants to certain other
               service providers.

               Employee means any person employed as a common law employee of
               the Company or an Eligible Subsidiary.

ADMINISTRATOR  The Administrator will be the Compensation Committee of the Board
               of Directors of COSTAR (the "Compensation Committee"), unless the
               Board specifies another committee. The Board may also act under
               the Plan as though it were the Compensation Committee.

               The Administrator is responsible for the general operation and
               administration of the Plan and for carrying out its provisions
               and has full discretion in interpreting and administering the
               provisions of the Plan. Subject to the express provisions of the
               Plan, the Administrator may exercise such powers and authority of
               the Board as the Administrator may find necessary or appropriate
               to carry out its functions. The Administrator may delegate its



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               functions (other than those described in the GRANTING OF AWARDS
               section) to officers or employees of COSTAR.











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               The Administrator's powers will include, but not be limited to,
               the power to amend, waive, or extend any provision or limitation
               of any Award. The Administrator may act through meetings of a
               majority of its members or by unanimous consent.

GRANTING OF    Subject to the terms of the Plan, the Administrator will, in
AWARDS         its sole discretion, determine

                              the participants who receive Awards,

                              the terms of such Awards,

                              the schedule for exercisability or
                              nonforfeitability (including any requirements that
                              the participant or the Company satisfy performance
                              criteria),

                              the time and conditions for expiration of the
                              Award, and

                              the form of payment due upon exercise, if any.

               The Administrator's determinations under the Plan need not be
               uniform and need not consider whether possible participants are
               similarly situated.

               Options granted to employees may be nonqualified stock options
               ("NQSOs") or "incentive stock options" ("ISOs") within the
               meaning of Section 422 of the Internal Revenue Code of 1986, as
               amended from time to time (the "Code"), or the corresponding
               provision of any subsequently enacted tax statute. Options
               granted to Eligible Directors must be NQSOs. The Administrator
               will not grant ISOs unless the stockholders have approved the
               Plan.

               The Administrator may impose such conditions on or charge such
               price for the Stock Grants as it deems appropriate.

SUBSTITUTIONS  The Administrator may also grant Awards in substitution for
               options or other equity interests held by individuals (i) as a
               result of their employment by or services to CoStar Group, L.P.
               or (ii) who become Employees of the Company or of an Eligible
               Subsidiary as a result of the Company's acquiring or merging with
               the individual's employer or acquiring its assets. If necessary
               to conform the Awards to the interests for which they are
               substitutes, the Administrator may grant substitute Awards under
               terms and conditions that vary from those the Plan otherwise
               requires.

DIRECTOR       Each Eligible Director of the Company shall be entitled to
FORMULA        receive at the first meeting of the Board of Directors
               immediately following each



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                                                              CoStar Group, Inc.
                                                       1998 Stock Incentive Plan
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OPTIONS        of the Company's Annual Meeting of Stockholders an Option to
               purchase 1,000 shares of the Company's Common Stock at an
               exercise price equal to the Fair Market Value (as defined below)
               on such date of grant. Such Options shall vest in full on the
               first anniversary of the date of grant, provided that such
               Director is still a Director of the Company.

DATE OF GRANT  The Date of Grant will be the date as of which this Plan or the
               Administrator grants an Award to a participant, as specified in
               the Plan or in the Administrator's minutes.

EXERCISE PRICE The Exercise Price is the value of the consideration that a
               participant must provide in exchange for one share of Common
               Stock. The Administrator will determine the Exercise Price under
               each Award and may set the Exercise Price without regard to the
               Exercise Price of any other Awards granted at the same or any
               other time. The Company may use the consideration it receives
               from the participant for general corporate purposes.

               The Exercise Price per share for NQSOs may not be less than 100%
               of the Fair Market Value of a share on the Date of Grant. If an
               Option is intended to be an ISO, the Exercise Price per share may
               not be less than 100% of the Fair Market Value (on the Date of
               Grant) of a share of Common Stock covered by the Option;
               provided, however, that if the Administrator decides to grant an
               ISO to someone covered by Sections 422(b)(6) and 424(d) (as a
               more-than-10%-stock-owner), the Exercise Price of the Option must
               be at least 110% of the Fair Market Value (on the Date of Grant).

               The Administrator may satisfy any state law requirements
               regarding adequate consideration for Stock Grants by (i) issuing
               Common Stock held as treasury stock or (ii) charging the
               recipients at least the par value for the shares covered by the
               Stock Grant. The Administrator may designate that a recipient may
               satisfy (ii) either by direct payments or by the Administrator's
               withholding from other payments due to the recipient.

FAIR MARKET    Fair Market Value of a share of Common Stock for purposes
VALUE          of the Plan will be determined as follows:

                              if the Common Stock is traded on a national
                              securities exchange, the closing sale price on
                              that date;

                              if the Common Stock is not traded on any such
                              exchange, the closing sale price as reported by
                              the National Association of Securities Dealers,
                              Inc. Automated Quotation System ("Nasdaq") for
                              such date;

                              if no such closing sale price information is
                              available, the average of the closing bid and
                              asked prices as reported by Nasdaq for such date;
                              or


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                                                       1998 Stock Incentive Plan
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                              if there are no such closing bid and asked prices,
                              the average of the closing bid and asked prices as
                              reported by any other commercial service for such
                              date.

               For any date that is not a trading day, the Fair Market Value of
               a share of Common Stock for such date shall be determined by
               using the closing sale price or the average of the closing bid
               and asked prices, as appropriate, for the immediately preceding
               trading day.

               The Fair Market Value will be deemed equal to the IPO price for
               any Options granted as of the date on which the IPO's
               underwriters price the IPO.

EXERCISABILITY The Administrator will determine the times and conditions for
               exercise of or purchase under each Award but may not extend the
               period for exercise beyond the tenth anniversary of its Date of
               Grant (or five years for ISOs granted to 10% owners covered by
               Code Sections 422(b)(6) and 424(d)).

               Awards will become exercisable at such times and in such manner
               as the Administrator determines and the Award Agreement, if any,
               indicates; provided, however, that the Administrator may, on such
               terms and conditions as it determines appropriate, accelerate the
               time at which the participant may exercise any portion of an
               Award or at which restrictions on Stock Grants lapse. For Stock
               Grants, "exercise" refers to acceptance of the Award or lapse of
               restrictions, as appropriate in context.

               If the Administrator does not specify otherwise, Options will
               become exercisable and restrictions on Stock Grants (other than
               the Director Formula Grants) will lapse as to one-third of the
               covered shares on each of the first, second, and third
               anniversaries of the Date of Grant.

               No portion of an Award that is unexercisable at a participant's
               termination of employment will thereafter become exercisable,
               unless the Award Agreement provides otherwise, either initially
               or by amendment.


CHANGE OF      Upon a Change of Control (as defined below), all Options held by
CONTROL        current Employees and directors will become fully exercisable and
               all restrictions on Stock Grants will lapse. A Change of Control
               for this purpose means the occurrence, after the Company's IPO,
               of any one or more of the following events:

                              a person, entity, or group (other than the
                              Company, any Company subsidiary, any Company
                              benefit plan, or any underwriter temporarily
                              holding securities for an offering of such
                              securities) acquires ownership


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                                                       1998 Stock Incentive Plan
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                              of more than 80% of the undiluted total voting
                              power of the Company's then-outstanding securities
                              eligible to vote to elect members of the Board
                              ("Company Voting Securities");

                              consummation of a merger or consolidation of the
                              Company into any other entity -- unless the
                              holders of the Company Voting Securities
                              outstanding immediately before such consummation,
                              together with any trustee or other fiduciary
                              holding securities under a Company benefit plan,
                              hold securities that represent immediately after
                              such merger or consolidation at least 20% of the
                              combined voting power of the then outstanding
                              voting securities of either the Company or the
                              other surviving entity or its parent; or

                              the stockholders of the Company approve (i) a plan
                              of complete liquidation or dissolution of the
                              Company or (ii) an agreement for the Company's
                              sale or disposition of all or substantially all
                              the Company's assets, and such liquidation,
                              dissolution, sale, or disposition is consummated.

                              Even if other tests are met, a Change of Control
                              has not occurred under any circumstance in which
                              the Company files for bankruptcy protection or is
                              reorganized following a bankruptcy filing.

               The ADJUSTMENT UPON CHANGES IN CAPITAL STOCK provisions will also
               apply if the Change of Control is a SUBSTANTIAL CORPORATE CHANGE
               (as defined in those provisions).

LIMITATION ON  An Option granted to an employee will be an ISO only to the
ISOs           extent that the aggregate Fair Market Value (determined at the
               Date of Grant) of the stock with respect to which ISOs are
               exercisable for the first time by the optionee during any
               calendar year (under the Plan and all other plans of the Company
               and its subsidiary corporations, within the meaning of Code
               Section 422(d)), does not exceed $100,000. This limitation will
               be applied by taking Options into account in the order in which
               such Options were granted. If, by design or operation, the Option
               exceeds this limit, the excess will be treated as an NQSO.

METHOD OF      To exercise any exercisable portion of an Award, the participant
EXERCISE       must:

                              Deliver a written notice of exercise to the
                              Secretary of the Company (or to whomever the
                              Administrator designates), in a form complying
                              with any rules the Administrator may issue, signed
                              by the participant, and specifying the number of
                              shares of Common Stock underlying the portion of
                              the Award the participant is exercising;


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                                                       1998 Stock Incentive Plan
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                              Pay the full Exercise Price, if any, by cashier's
                              or certified check for the shares of Common Stock
                              with respect to which the Award is being
                              exercised, unless the Administrator consents to
                              another form of payment (which could include the
                              use of Common Stock); and

                              Deliver to the Administrator such representations
                              and documents as the Administrator, in its sole
                              discretion, may consider necessary or advisable.

               Payment in full of the Exercise Price need not accompany the
               written notice of exercise provided the notice directs that the
               stock certificates for the shares issued upon the exercise be
               delivered to a licensed broker acceptable to the Company as the
               agent for the individual exercising the option and at the time of
               closing of the sale of the Common Stock issued upon exercise of
               the Option, the broker will tender to the Company cash or cash
               equivalents acceptable to the Company and equal to the Exercise
               Price.

               If the Administrator agrees to payment through the tender to the
               Company of shares of Common Stock, the individual must have held
               the stock being tendered for at least six months at the time of
               surrender. Shares of stock offered as payment will be valued, for
               purposes of determining the extent to which the participant has
               paid the Exercise Price, at their Fair Market Value on the date
               of exercise. The Administrator may also, in its discretion,
               accept attestation of ownership of Common Stock and issue a net
               number of shares upon Option exercise.

AWARD          No one may exercise an Award more than ten years after its Date
EXPIRATION     of Grant (or five years, for an ISO granted to a more-than-10%
               shareholder). Unless the Award Agreement provides otherwise,
               either initially or by amendment, no one may exercise an Award
               after the first to occur of:

          EMPLOYMENT          The 90th day after the date of termination of
          TERMINATION         employment (other than for death or Disability),
                              where termination of employment means the time
                              when the employer-employee or other
                              service-providing relationship between the
                              employee and the Company ends for any reason,
                              including retirement. Unless the Award Agreement
                              provides otherwise, termination of employment does
                              not include instances in which the Company
                              immediately rehires a common law employee as an
                              independent contractor. The Administrator, in its
                              sole discretion, will determine all questions of
                              whether particular terminations or leaves of
                              absence are terminations of employment;

          DISABILITY          For disability, the earlier of (i) the first
                              anniversary of the participant's termination of
                              employment for disability and (ii) thirty (30)
                              days after the participant no longer has a
                              disability, where "disability" means the


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                                                       1998 Stock Incentive Plan
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                              inability to engage in any substantial gainful
                              activity by reason of any medically determinable
                              physical or mental impairment that can be expected
                              to result in death or that has lasted or can be
                              expected to last for a continuous period of not
                              less than twelve months; or

          DEATH               The date twelve months after the participant's
                              death.

               If exercise is permitted after termination of employment, the
               Award will nevertheless expire as of the date that the former
               service provider violates any covenant not to compete in effect
               between the Company and the former employee. In addition, an
               optionee who exercises an Option more than 90 days after
               termination of employment with the Company and/or the Eligible
               Subsidiaries will only receive ISO treatment to the extent
               permitted by law, and becoming or remaining an employee of
               another related company (that is not an Eligible Subsidiary) or
               an independent contractor to the Company will not prevent loss of
               ISO status as a result of the formal termination of employment.

               Nothing in this Plan extends the term of an Award beyond the
               tenth anniversary of its Date of Grant, nor does anything in this
               AWARD EXPIRATION section make an Award exercisable that has not
               otherwise become exercisable.

AWARD          Option Agreements will set forth the terms of each Option and
AGREEMENT      will include such terms and conditions, consistent with the Plan,
               as the Administrator may determine are necessary or advisable. To
               the extent the agreement is inconsistent with the Plan, the Plan
               will govern. The Option Agreements may contain special rules. The
               Administrator may, but is not required to, issue agreements for
               Stock Grants.

STOCK SUBJECT  Except as adjusted below under CORPORATE CHANGES, the aggregate
TO PLAN        number of shares of Common Stock that may be issued under
               the Awards (whether ISOs, NQSOs, or Stock Grants) may not exceed
               2,050,000 shares and the maximum number of shares that may be
               granted under Awards for a single individual in a calendar year
               may not exceed 400,000 shares. (The individual maximum applies
               only to Awards first made under this Plan and not to Awards made
               in substitution of a prior employer's options or other
               incentives, except as Code Section 162(m) otherwise requires.)
               The Common Stock will come from either authorized but unissued
               shares or from previously issued shares that the Company
               reacquires, including shares it purchases on the open market. If
               any Award expires, is canceled, or terminates for any other
               reason, the shares of Common Stock available under that Award
               will again be available for the granting of new Awards (but will
               be counted against that calendar year's limit for a given
               individual).


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                                                       1998 Stock Incentive Plan
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               No adjustment will be made for a dividend or other right for
               which the record date precedes the date of exercise.

               The participant will have no rights of a stockholder with respect
               to the shares of stock subject to an Award except to the extent
               that the Company has issued certificates for, or otherwise
               confirmed ownership of, such shares upon the exercise of the
               Award.

               The Company will not issue fractional shares pursuant to the
               exercise of an Award, but the Administrator may, in its
               discretion, direct the Company to make a cash payment in lieu of
               fractional shares.

PERSON WHO     During the participant's lifetime, only the participant or
MAY EXERCISE   his duly appointed guardian or personal representative may
               exercise the Awards. After his death, his personal representative
               or any other person authorized under a will or under the laws of
               descent and distribution may exercise any then exercisable
               portion of an Award. If someone other than the original recipient
               seeks to exercise any portion of an Award, the Administrator may
               request such proof as it may consider necessary or appropriate of
               the person's right to exercise the Award.

ADJUSTMENTS    Subject to any required action by the Company (which it shall
UPON CHANGES   promptly take) or its stockholders, and subject to the provisions
IN CAPITAL     of applicable corporate law, if, after the Date of Grant of an
STOCK          Award,

                              the outstanding shares of Common Stock increase or
                              decrease or change into or are exchanged for a
                              different number or kind of security by reason of
                              any recapitalization, reclassification, stock
                              split, reverse stock split, combination of shares,
                              exchange of shares, stock dividend, or other
                              distribution payable in capital stock, or

                              some other increase or decrease in such Common
                              Stock occurs without the Company's receiving
                              consideration,

               the Administrator may make a proportionate and appropriate
               adjustment in the number of shares of Common Stock underlying
               each Award, so that the proportionate interest of the participant
               immediately following such event will, to the extent practicable,
               be the same as immediately before such event. (This adjustment
               does not apply to Common Stock that the optionee has already
               purchased nor to Stock Grants that are already nonforfeitable,
               except to the extent of similar treatment for all stockholders.)
               Unless the Administrator determines another method would be
               appropriate, any such adjustment to an Award will not change the
               total price with respect to shares of Common Stock underlying the
               unexercised portion of the Award but will



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                                                       1998 Stock Incentive Plan
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               include a corresponding proportionate adjustment in the Award's
               Exercise Price.

               The Administrator will make a commensurate change to the maximum
               number and kind of shares provided in the STOCK SUBJECT TO PLAN
               section.

               Any issue by the Company of any class of preferred stock, or
               securities convertible into shares of common or preferred stock
               of any class, will not affect, and no adjustment by reason
               thereof will be made with respect to, the number of shares of
               Common Stock subject to any Award or the Exercise Price except as
               this ADJUSTMENTS section specifically provides. The grant of an
               Award under the Plan will not affect in any way the right or
               power of the Company to make adjustments, reclassifications,
               reorganizations or changes of its capital or business structure,
               or to merge or to consolidate, or to dissolve, liquidate, sell,
               or transfer all or any part of its business or assets.

SUBSTANTIAL    Upon a Substantial Corporate Change, the Plan and any unexercised
CORPORATE      Awards will terminate unless provision is made in writing in
CHANGE         connection with such transaction for

                              the assumption or continuation of outstanding
                              Awards, or

                              the substitution for such options or grants of
                              any options or grants covering the stock or
                              securities of a successor employer corporation,
                              or a parent or subsidiary of such successor, with
                              appropriate adjustments as to the number and kind
                              of shares of stock and prices, in which event the
                              Awards will continue in the manner and under the
                              terms so provided.

               Unless the Board determines otherwise, if an Award would
               otherwise terminate pursuant to the preceding sentence,
               participants who are then Employees or directors of the Company
               will have the right, at such time before the consummation of the
               transaction causing such termination as the Board reasonably
               designates, to exercise any unexercised portions of the Award,
               whether or not they had previously become exercisable. However,
               unless the Board determines otherwise, the acceleration will not
               occur if it would render unavailable "pooling of interest"
               accounting for any reorganization, merger, or consolidation of
               the Company.

               A Substantial Corporate Change means the

                              dissolution or liquidation of the Company,

                              merger, consolidation, or reorganization of the
                              Company with one or more corporations in which the
                              Company is not the surviving corporation,



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                              the sale of substantially all of the assets of the
                              Company to another corporation, or

                              any transaction (including a merger or
                              reorganization in which the Company survives)
                              approved by the Board that results in any person
                              or entity (other than any affiliate of the Company
                              as defined in Rule 144(a)(1) under the Securities
                              Act) owning 100% of the combined voting power of
                              all classes of stock of the Company.

SUBSIDIARY     Employees of Company Subsidiaries will be entitled to participate
EMPLOYEES      in the Plan, except as otherwise designated by the Board of
               Directors or the Committee.

               Eligible Subsidiary means each of the Company's Subsidiaries,
               except as the Board otherwise specifies. For ISO grants,
               Subsidiary means any corporation (other than the Company) in an
               unbroken chain of corporations beginning with the Company if, at
               the time an ISO is granted to a Participant under the Plan, each
               of the corporations (other than the last corporation in the
               unbroken chain) owns stock possessing 50% or more of the total
               combined voting power of all classes of stock in one of the other
               corporations in such chain. For NQSOs, the Board or the Committee
               can use a different definition of Subsidiary in its discretion.

LEGAL          The Company will not issue any shares of Common Stock under an
COMPLIANCE     Award until all applicable requirements imposed by Federal and
               state securities and other laws, rules, and regulations, and by
               any applicable regulatory agencies or stock exchanges, have been
               fully met. To that end, the Company may require the participant
               to take any reasonable action to comply with such requirements
               before issuing such shares. No provision in the Plan or action
               taken under it authorizes any action that is otherwise prohibited
               by Federal or state laws.

               The Plan is intended to conform to the extent necessary with all
               provisions of the Securities Act of 1933 ("Securities Act") and
               the Exchange Act and all regulations and rules the Securities and
               Exchange Commission issues under those laws. Notwithstanding
               anything in the Plan to the contrary, the Administrator must
               administer the Plan, and Awards may be granted and exercised,
               only in a way that conforms to such laws, rules, and regulations.
               To the extent permitted by applicable law, the Plan and any
               Awards will be deemed amended to the extent necessary to conform
               to such laws, rules, and regulations.

PURCHASE FOR   Unless a registration statement under the Securities Act
INVESTMENT     covers the shares of Common Stock a participant receives upon
               exercise of his


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                                                       1998 Stock Incentive Plan
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AND OTHER      Award, the Administrator may require, at the time of such
RESTRICTIONS   exercise or receipt of a grant, that the participant agree in
               writing to acquire such shares for investment and not for public
               resale or distribution, unless and until the shares subject to
               the Award are registered under the Securities Act. Unless the
               shares are registered under the Securities Act, the participant
               must acknowledge:

                              that the shares purchased on exercise of the Award
                              are not so registered,

                              that the participant may not sell or otherwise
                              transfer the shares unless

                                             the shares have been registered
                                             under the Securities Act in
                                             connection with the sale or
                                             transfer thereof, or

                                             counsel satisfactory to the Company
                                             has issued an opinion satisfactory
                                             to the Company that the sale or
                                             other transfer of such shares is
                                             exempt from registration under the
                                             Securities Act, and

                                             such sale or transfer complies with
                                             all other applicable laws, rules,
                                             and regulations, including all
                                             applicable Federal and state
                                             securities laws, rules, and
                                             regulations.

               Additionally, the Common Stock, when issued upon the exercise of
               an Award, will be subject to any other transfer restrictions,
               rights of first refusal, and rights of repurchase set forth in or
               incorporated by reference into other applicable documents,
               including the Company's articles or certificate of incorporation,
               by-laws, or generally applicable stockholders' agreements.

               The Administrator may, in its sole discretion, take whatever
               additional actions it deems appropriate to comply with such
               restrictions and applicable laws, including placing legends on
               certificates and issuing stop-transfer orders to transfer agents
               and registrars.

TAX            The participant must satisfy all applicable Federal, state, and
WITHHOLDING    local income and employment tax withholding requirements before
               the Company will deliver stock certificates upon the exercise of
               an Award. The Company may decide to satisfy the withholding
               obligations through additional withholding on salary or wages. If
               the Company does not or cannot withhold from other compensation,
               the participant must pay the Company, with a cashier's check or
               certified check, the full amounts required by withholding.
               Payment of withholding obligations is due before the Company
               issues shares with respect to the Award. If the Committee so
               determines, the participant may instead satisfy the withholding
               obligations by directing the Company to retain shares from the



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                                                       1998 Stock Incentive Plan
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               Award exercise, by tendering previously owned shares, or by
               attesting to his ownership of shares (with the distribution of
               net shares).

TRANSFERS,     Unless the Administrator otherwise approves in advance in
ASSIGNMENTS    writing, an Award may not be assigned, pledged, or otherwise
AND PLEDGES    transferred in any way, whether by operation of law or
               otherwise or through any legal or equitable proceedings
               (including bankruptcy), by the participant to any person, except
               by will or by operation of applicable laws of descent and
               distribution. If Rule 16b-3 then applies to an Award, the
               participant may not transfer or pledge shares of Common Stock
               acquired under a Stock Grant or upon exercise of an Option until
               at least six (6) months have elapsed from (but excluding) the
               Date of Grant, unless the Administrator approves otherwise in
               advance in writing.

AMENDMENT OR   The Board may amend, suspend, or terminate the Plan at any
TERMINATION    time, without the consent of the participants or their
OF PLAN AND    beneficiaries; provided, however, that no amendment will deprive
OPTIONS        any participant or beneficiary of any previously declared Award.
               Except as required by law or by the CORPORATE CHANGES section,
               the Administrator may not, without the participant's or
               beneficiary's consent, modify the terms and conditions of an
               Award so as to adversely affect the participant. No amendment,
               suspension, or termination of the Plan will, without the
               participant's or beneficiary's consent, terminate or adversely
               affect any right or obligations under any outstanding Awards.

PRIVILEGES OF  No participant and no beneficiary or other person claiming
STOCK          under or through such participant will have any right, title, or
OWNERSHIP      interest in or to any shares of Common Stock allocated or
               reserved under the Plan or subject to any Award except as to such
               shares of Common Stock, if any, that have been issued to such
               participant.

EFFECT ON      Whether exercising or receiving an Award causes the
OTHER PLANS    participant to accrue or receive additional benefits under any
               pension or other plan is governed solely by the terms of such
               other plan.

LIMITATIONS ON Notwithstanding any other provisions of the Plan, no
LIABILITY      individual acting as a director, employee, or agent of the
               Company shall be liable to any participant, former participant,
               spouse, beneficiary, or any other person for any claim, loss,
               liability, or expense incurred in connection with the Plan, nor
               shall such individual be personally liable because of any
               contract or other instrument he executes in such other capacity.
               The Company will indemnify and hold harmless each director,
               employee, or agent of the Company to whom any duty or power
               relating to the administration or interpretation of the Plan has
               been or will be delegated, against any cost or expense (including
               attorneys' fees) or liability (including any sum paid in
               settlement of a claim with the


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                                                              CoStar Group, Inc.
                                                       1998 Stock Incentive Plan
   14

               Board's approval) arising out of any act or omission to act
               concerning this Plan unless arising out of such person's own
               fraud or bad faith.

NO EMPLOYMENT  Nothing contained in this Plan constitutes an employment contract
CONTRACT       between the Company and the participants. The Plan does not give
               any participant any right to be retained in the Company's employ,
               nor does it enlarge or diminish the Company's right to terminate
               the participant's employment.

APPLICABLE LAW The laws of the State of Delaware (other than its choice of
               law provisions) govern this Plan and its interpretation.

DURATION       Unless the Board extends the Plan's term, the Administrator may
OF PLAN        not grant Awards after May 8, 2008. The Plan will then terminate
               but will continue to govern unexercised and unexpired Awards.





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                                                              CoStar Group, Inc.
                                                       1998 Stock Incentive Plan