COSTARGROUP,INC. 1998 STOCKINCENTIVEPLAN (ASLAST AMENDED ONJUNE 18, 2002)

EXHIBIT 10.1

COSTAR GROUP, INC.
1998 STOCK INCENTIVE PLAN
(AS LAST AMENDED ON JUNE 18, 2002)

I.    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”).

II.    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.

III.    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 functions (other than those described in the Granting of Awards section) to officers or employees of CoStar.

         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.

IV.     Granting of Awards

         Subject to the terms of the Plan, the Administrator will, in its sole discretion, determine:

         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 Realty Information 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.

V.     Director Automatic Option Grants

         At the first meeting of the Board of Directors following each annual meeting of stockholders, the Chairman of the Board of Directors and each non-employee director serving on the Board of Directors shall receive an annual automatic grant of options to purchase 5,000 shares of Common Stock of the Company. These options shall have an exercise price equal to the Fair Market Value (as defined below) of the Common Stock on the date of grant, and one-fourth of the options will vest and become exercisable on each anniversary of the date of grant, as long as such director is still serving on the Company’s Board of Directors on such vesting date.

         In addition, at the first meeting of the Board of Directors following each annual meeting of stockholders, the Chairman of each Board committee of the Company shall receive an annual automatic grant of options to purchase 1,000 shares of Common Stock of the Company. These options shall have an exercise price equal to the Fair Market Value of the Common Stock on the date of grant, and one-fourth of the options will vest and become exercisable on each anniversary of the date of grant, as long as such director is still serving on the Company’s Board of Directors on such vesting date.

VI.     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.

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VII.    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 Value. Fair Market Value of a share of Common Stock for purposes of the Plan will be determined as follows:

         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.

VIII.    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)).

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         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 Control. Upon a Change of Control (as defined below), all Options held by 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:

         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).

IX.     Limitation on ISOs

         An Option granted to an employee will be an ISO only to the 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

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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.

X.     Method of Exercise

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

         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.

XI.    Award Expiration

         No one may exercise an Award more than ten years after its Date 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 Termination. The 90th day after the date of termination of 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

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“disability” means the 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

         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.

XII.    Award Agreement

         Option Agreements will set forth the terms of each Option and 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.

XIII.    Stock Subject to Plan

         Except as adjusted below under Corporate Changes, the aggregate number of shares of Common Stock that may be issued under the Awards (whether ISOs, NQSOs, or Stock Grants) may not exceed 3,750,000 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).

         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.

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XIV.    Person Who May Exercise

         During the participant’s lifetime, only the participant or 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.

XV.    Adjustments upon Changes in Capital Stock

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

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

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         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.

XVI.    Subsidiary Employees

         Employees of Company Subsidiaries will be entitled to participate 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.

XVII.    Legal Compliance

         The Company will not issue any shares of Common Stock under an 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.

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         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.

XVIII.    Purchase for Investment and Other Restrictions

         Unless a registration statement under the Securities Act covers the shares of Common Stock a participant receives upon exercise of his Award, the Administrator may require, at the time of such 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:

         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.

XIX.    Tax Withholding

         The participant must satisfy all applicable Federal, state, and 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

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retain shares from the Award exercise, by tendering previously owned shares, or by attesting to his ownership of shares (with the distribution of net shares).

XX.     Transfers, Assignments and Pledges

         Unless the Administrator otherwise approves in advance in writing, an Award may not be assigned, pledged, or otherwise 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.

XXI.    Amendment or Termination of Plan and Options

         The Board may amend, suspend, or terminate the Plan at any time, without the consent of the participants or their beneficiaries; provided, however, that no amendment will deprive 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.

XXII.    Privileges of Stock Ownership

         No participant and no beneficiary or other person claiming under or through such participant will have any right, title, or 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.

XXIII.    Effect on Other Plans

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

XXIV.    Limitations on Liability

         Notwithstanding any other provisions of the Plan, no 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 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.

XXV.    No Employment Contract

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         Nothing contained in this Plan constitutes an employment 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.

XXVI.    Applicable Law

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

XXVII.    Duration of Plan

         Unless the Board extends the Plan’s term, the Administrator may 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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