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                                                                     EXHIBIT 4.5

[USi LOGO]                                                          CONFIDENTIAL

                             USINTERNETWORKING, INC.
                        2000 EMPLOYEE STOCK PURCHASE PLAN

                                   ARTICLE I.
                  PURPOSE, SCOPE AND ADMINISTRATION OF THE PLAN

1.1    Purpose and Scope

       The purpose of the USinternetworking, Inc. 2000 Employee Stock Purchase
Plan is to assist employees of USinternetworking, Inc. and its subsidiaries in
acquiring a stock ownership interest in the Company pursuant to a plan which is
intended to qualify as an "employee stock purchase plan" under Section 423 of
the Internal Revenue Code of 1986, as amended.

1.2    Administration of Plan

       The Plan shall be administered by the Committee. The Committee shall have
the power to make, amend and repeal rules and regulations for the interpretation
and administration of the Plan consistent with the qualification of the plan
under Section 423 of the Code, and the Committee also is authorized to change
the Option Periods, Offering Dates and Exercise Dates under the Plan by
providing written notice to all Employees at least 15 days prior to the date
following which such changes will take effect. The Committee may delegate
administrative tasks under the Plan to one or more Officers of the Company. The
Committee's interpretation and decisions in respect to the Plan shall be final
and conclusive.

                                   ARTICLE II.
                                   DEFINITIONS

       Whenever the following terms are used in this Plan, they shall have the
meaning specified below unless the context clearly indicates to the contrary.
The singular pronoun shall include the plural where the context so indicates.

2.1    "Board" shall mean the Board of Directors of the Company.

2.2    "Code" shall mean the Internal Revenue Code of 1986, as amended.

2.3    "Committee" shall mean the Compensation Committee of the Board, which
Committee shall administer the Plan as provided in Section 1.2 above.

2.4    "Common Stock" shall mean shares of common stock of the Company.

2.5    "Company" shall mean USinternetworking, Inc.

2.6    "Compensation" shall mean the base salary, bonuses, overtime and
commissions paid to an Employee by the Company or a Subsidiary in accordance
with established payroll procedures.


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[USi LOGO]                                                          CONFIDENTIAL

2.7    "Eligible Employee" shall mean an Employee who (a) is customarily
scheduled to work at least 20 hours per week and (b) whose customary employment
is more than five (5) months in a calendar year.

2.8    "Employee" shall mean any employee of the Company or a Subsidiary.

2.9    "Exercise Date" shall mean each February 28 (or, each leap year, February
29) and August 31.

2.10   "Exchange Act" shall mean the Securities Exchange Act of 1934, as
amended.

2.11   "Fair Market Value" of a share of Common Stock as of a given date shall
mean (i) the closing price of the sale of Common Stock on the Nasdaq National
Market System ("Nasdaq") as of 4:00 P.M., New York time on such date or on the
immediately preceding trading date, or (ii) if Common Stock is not quoted on
Nasdaq, the fair market value of a share of Common Stock as established by the
Committee acting in good faith.

2.12   "Offering Date" shall mean each March 1 and September 1; provided,
however, that the first Offering Date under the Plan shall be March 24, 2000.

2.13   "Officer" shall mean an employee of the Company who is either an
executive officer or member of the management of the Company.

2.14   "Option Period" shall mean the period beginning on an Offering Date and
ending on the next succeeding Exercise Date.

2.15   "Option Price" shall mean the purchase price of a share of Common Stock
hereunder as provided in Section 4.1 below.

2.16   "Participant" shall mean any Eligible Employee who elects to participate.

2.17   "Plan" shall mean this USinternetworking, Inc. 2000 Employee Stock
Purchase Plan, as it may be amended from time to time.

2.18   "Plan Account" shall mean a bookkeeping account established and
maintained by the Company in the name of each Participant.

2.19   "Subsidiary" shall mean any corporation of which the Company or a
Subsidiary owns stock possessing 50% or more of the total combined voting power
of all classes of stock in the corporation.


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[USi LOGO]                                                          CONFIDENTIAL

                                  ARTICLE III.
                                  PARTICIPATION

3.1    Eligibility

       An Eligible Employee may participate in the Plan if immediately after the
applicable Offering Date, that Employee would not be deemed for purposes of
Section 423(b)(3) of the Code to possess 5% or more of the total combined voting
power or value of all classes of stock of the Company or any Subsidiary.

3.2    Election to Participate; Payroll Deductions

       (a)    An Eligible Employee may participate in the Plan only by means of
payroll deduction. An Eligible Employee may elect to participate in the Plan
during an Option Period by delivering to the Company in the calendar month
preceding the Offering Date on which such Option Period commences a written
payroll deduction authorization on a form prescribed by the Company; provided,
however that for the Option Period commencing on the March 24, 2000, an Eligible
Employee may elect to participate in the Plan at any time on or prior to the
March 24, 2000.

       (b)    Payroll deductions (i) shall be equal to at least 1%, but not more
than 15%, of the Participant's Compensation as of the Offering Date; (ii) must
equal at least five dollars ($5.00) per pay period; and (iii) may be expressed
either as (A) a whole number percentage or (B) a fixed dollar amount, subject to
the provisions of Sections 4.2 and 4.3 below. Amounts deducted from a
Participant's Compensation pursuant to this Section 3.2 shall be credited to the
Participant's Plan Account.

3.3    Leave of Absence

       During leaves of absence approved by the Company meeting the requirements
of Regulation Section 1.421-7(h)(2) under the Code, a Participant may continue
participation in the Plan by making cash payments to the Company on his or her
normal payday equal to his or her authorized payroll deduction.

                                   ARTICLE IV.
                               PURCHASE OF SHARES

4.1    Option Price

       The Option Price per share of the Common Stock sold to Participants
hereunder shall be 85% of the Fair Market Value of such share on either the
Offering Date or the Exercise Date of the Option Period, whichever is lower, but
in no event shall the Option Price per share be less than the par value per
share ($0.001) of the Common Stock.


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[USi LOGO]                                                          CONFIDENTIAL

4.2    Purchase of Shares

       (a)    On each Exercise Date on which he or she is employed, each
Participant will automatically and without any action on his or her part be
deemed to have exercised his or her option to purchase at the Option Price the
largest number of whole shares of Common Stock which can be purchased with the
amount in the Participant's Plan Account. The balance, if any, remaining in the
Participant's Plan Account (after exercise of his or her option) as of an
Exercise Date shall be carried forward to the next Option Period, unless the
Participant has elected to withdraw from the Plan pursuant to Section 6.1 below.

       (b)    As soon as practicable following each Exercise Date, the Company
will deliver to the Participant a certificate issued in his or her name for such
number of shares purchased by such Participant pursuant to subsection (a) above.
In the event the Company is required to obtain from any commission or agency
authority to issue any such certificate, the Company will seek to obtain such
authority. Inability of the Company to obtain from any such commission or agency
authority which counsel for the Company deems necessary for the lawful issuance
of any such certificate shall relieve the Company from liability to any
Participant except to refund to him or her the amount withheld.

4.3    Limitations on Purchase

       No Employee shall be granted an option under the Plan which permits his
or her rights to purchase Common Stock under the Plan or any other employee
stock purchase plan of the Company or any of its Subsidiaries to accrue at a
rate which exceeds $25,000 (as measured by the Fair Market Value of such Common
Stock at the time the option is granted) for each calendar year such option is
outstanding. For purposes of this Section 4.3, the right to purchase Common
Stock under an option accrues when the option (or any portion thereof) becomes
exercisable, and the right to purchase Common Stock which has accrued under one
option under the Plan may not be carried over to any other option.

4.4    Transferability of Rights

       An option granted under the Plan shall not be transferable and is
exercisable only by the Participant. No option or interest or right to the
option shall be available to pay off any debts, contracts or engagements of the
Participant or his or her successors in interest or shall be subject to
disposition by pledge, encumbrance, assignment or any other means whether such
disposition be voluntary or involuntary or by operation of law by judgment,
levy, attachment, garnishment or any other legal or equitable proceedings
(including bankruptcy), and any attempt at disposition of the option shall have
no effect.


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[USi LOGO]                                                          CONFIDENTIAL

                                   ARTICLE V.
                       PROVISIONS RELATING TO COMMON STOCK

5.1    Common Stock Reserved

       Subject to adjustment as provided in Section 5.2, the maximum number of
shares of Common Stock that shall be made available for sale under this Plan
shall be 1,500,000, plus an annual increase on the first day of each of the
Company's fiscal years beginning in 2001 and ending in 2010, equal to the lesser
of (a) 1,000,000 shares, (b) 0.75% of the shares outstanding on the last day of
the immediately preceding fiscal year, or (c) such lesser number of shares as is
determined by the Board. Shares of Common Stock made available for sale under
this Plan may be authorized but unissued or reacquired shares reserved for
issuance under this Plan.

5.2    Adjustment for Changes in Common Stock

       In the event that adjustments are made in the number of outstanding
shares of Common Stock or the shares are exchanged for a different class of
stock of the Company by reason of stock dividend, stock split or other
subdivision, the Committee shall make appropriate adjustments in (a) the number
and class of shares or other securities that may be reserved for purchase
hereunder and (b) the Option Price of outstanding options.

5.3    Merger, Acquisition or Liquidation

       In the event of the merger or consolidation of the Company into another
corporation, the acquisition by another corporation of all or substantially all
of the Company's assets or 80% or more of the Company's then outstanding voting
stock or the liquidation or dissolution of the Company, the date of exercise
with respect to outstanding options shall be the business day immediately
preceding the effective date of such merger, consolidation, acquisition,
liquidation or dissolution unless the Committee shall, in its sole discretion,
provide for the assumption or substitution of such options in a manner complying
with Section 424(a) of the Code.

5.4    Insufficient Shares

       If the aggregate funds available for the purchase of Common Stock on any
Exercise Date would cause an issuance of shares in excess of the number provided
for in Section 5.1 above, (a) the Committee shall proportionately reduce the
number of shares that would otherwise be purchased by each Participant in order
to eliminate such excess, and (b) the Plan shall automatically terminate
immediately after such Exercise Date.

5.5    Rights as Stockholders

       With respect to shares of Common Stock subject to an option, a
Participant shall not be deemed to be a stockholder and shall not have any of
the rights or privileges of a stockholder. A


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[USi LOGO]                                                          CONFIDENTIAL

Participant shall have the rights and privileges of a stockholder when, but not
until, a certificate has been issued to him or her following exercise of his or
her option.

                                   ARTICLE VI.
                          TERMINATION OF PARTICIPATION

6.1    Cessation of Contributions; Voluntary Withdrawal

       (a)    A Participant may cease payroll deductions during an Option Period
by delivering written notice of such cessation to the Company. Upon any such
cessation, the Participant may elect either to withdraw from the Plan pursuant
to subsection (b) below or to have amounts credited to his or her Plan Account
held in the Plan for the purchase of Common Stock pursuant to Section 4.2. A
Participant who ceases contributions to the Plan during any Option Period shall
not be permitted to resume contributions to the Plan during that Option Period.

       (b)    A Participant may withdraw from the Plan at any time by written
notice to the Secretary of the Company prior to the close of business on an
Exercise Date. Within 21 days after the notice of withdrawal is delivered, the
Company shall refund the entire amount, if any, in a Participant's Plan Account
to him or her, at which time, the Participant's payroll deduction authorization,
his or her interest in the Plan and his or her option under the Plan shall
terminate. Any Eligible Employee who withdraws from the Plan may again become a
Participant in accordance with Section 3.2 above.

6.2    Termination of Eligibility

       (a)    If a Participant ceases to be eligible under Section 3.1 above for
any reason, the amount in such Participant's Plan Account will be refunded to
the Participant or his or her designated beneficiary or estate within 21 days of
his or her termination of employment or other cessation of eligibility.

       (b)    Upon payment by the Company to the Participant or his or her
beneficiary or estate of the remaining balance, if any, in Participant's Plan
Account, the Participant's interest in the Plan and the Participant's option
under the Plan shall terminate.

                                  ARTICLE VII.
                               GENERAL PROVISIONS

7.1    Condition of Employment

       Neither the creation of the Plan nor an Employee's participation therein
shall be deemed to create a contract of employment, any right of continued
employment or in any way affect the right of the Company or a Subsidiary to
terminate an Employee at any time with or without cause.


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[USi LOGO]                                                          CONFIDENTIAL

7.2    Amendment of the Plan

       (a)    The Board may amend, suspend or terminate the Plan at any time and
from time to time; provided, however, that without approval of the Company's
stockholders given within 12 months before or after action by the Board, the
Plan may not be amended to increase the maximum number of shares subject to the
Plan or change the designation or class of Eligible Employees.

       (b)    Upon termination of the Plan, the balance in each Participant's
Plan Account shall be refunded within 21 days of such termination.

7.3    Use of Funds; No Interest Paid

       All funds received by the Company by reason of purchase of Common Stock
under this Plan will be included in the general funds of the Company free of any
trust or other restriction and may be used for any corporate purpose. No
interest will be paid to any Participant or credited under the Plan.

7.4    Term; Approval by Stockholders

       The Plan shall terminate on the tenth anniversary of the date of its
initial approval by the stockholders of the Company, unless earlier terminated
by action of the Board. No option may be granted during any period of suspension
of the Plan nor after termination of the Plan. The Plan will be submitted for
the approval of the Company's stockholders within 12 months after the date of
the Board's initial adoption of the Plan. Options may be granted prior to such
stockholder approval; provided, however, that such options shall not be
exercisable prior to the time when the Plan is approved by the stockholders;
provided further that if such approval has not been obtained by the end of said
12-month period, all options previously granted under the Plan shall thereupon
be canceled and become null and void.

7.5    Effect Upon Other Plans

       The adoption of the Plan shall not affect any other compensation or
incentive plans in effect for the Company or any Subsidiary. Nothing in this
Plan shall be construed to limit the right of the Company or any Subsidiary (a)
to establish any other forms of incentives or compensation for employees of the
Company or any Subsidiary or (b) to grant or assume options otherwise than under
this Plan in connection with any proper corporate purpose, including, but not by
way of limitation, the grant or assumption of options in connection with the
acquisition, by purchase, lease, merger, consolidation or otherwise, of the
business, stock or assets of any corporation, firm or association.


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[USi LOGO]                                                          CONFIDENTIAL

7.6    Conformity to Securities Laws

       Notwithstanding any other provision of this Plan, this Plan and the
participation in this Plan by any individual who is then subject to Section 16
of the Exchange Act shall be subject to any additional limitations set forth in
any applicable exemptive rule under Section 16 of the Exchange Act (including
any amendment to Rule 16b-3 of the Exchange Act) that are requirements for the
application of such exemptive rule. To the extent permitted by applicable law,
the Plan shall be deemed amended to the extent necessary to conform to such
applicable exemptive rule.

7.7    Notice of Disposition of Shares

       The Company may require any Participant to give the Company prompt notice
of any disposition of shares of Common Stock, acquired pursuant to the Plan,
within two years after the applicable Offering Date or within one year after the
applicable Exercise Date with respect to such shares. The Company may direct
that the certificates evidencing shares acquired pursuant to the Plan refer to
such requirement.

7.8    Tax Withholding

       The Company shall be entitled to require payment in cash or deduction
from other compensation payable to each Participant of any sums required by
federal, state or local tax law to be withheld with respect to any purchase of
shares of Common Stock under the Plan or any sale of such shares.

7.9    Governing Law

       The Plan and all rights and obligations thereunder shall be construed and
enforced in accordance with the laws of the State of Delaware.

                                   * * * * * *

       I hereby certify that the foregoing USinternetworking, Inc. 2000 Employee
Stock Purchase Plan was duly approved by the Compensation Committee of the Board
of Directors of USinternetworking, Inc. on December 21, 1999.

       I hereby certify that the foregoing USinternetworking, Inc. 2000 Employee
Stock Purchase Plan was duly approved by the stockholders of USinternetworking,
Inc. on _________ ___, 2000.

       Executed on this ___ day of ___________, 2000.



                                                     ---------------------------
                                                             Secretary


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