Prospect Acquisition Corp. Specimen Unit Certificate Representing Common Stock and Warrants

Exhibit 4.1

[SPECIMEN UNIT CERTIFICATE]

PROSPECT ACQUISITION CORP.
Incorporated Under the Laws of the State of Delaware

SEE REVERSE FOR
CERTAIN DEFINITIONS

UNITS CONSISTING OF ONE SHARE OF COMMON STOCK AND
ONE WARRANT EACH TO PURCHASE ONE SHARE OF COMMON STOCK

This certifies that                        is the owner of                        Units.

Each Unit ("Unit") consists of one (1) share of common stock, par value $0.0001 per share ("Common Stock"), of Prospect Acquisition Corp., a Delaware corporation (the "Company"), and one warrant (each a "Warrant"). Each Warrant entitles the holder to purchase one (1) share of Common Stock for $7.50 per share (subject to adjustment). Each Warrant will become exercisable on the later of (i) the Company's completion of a merger, capital stock exchange, asset acquisition or other similar business combination and (ii)                          , 2009, and will expire unless exercised before 5:00 p.m., New York time, on                        , 2012, or earlier upon redemption. The Common Stock and Warrants comprising the Units represented by this certificate are not transferable separately prior to                        , 2007 unless Citigroup Global Markets, Inc. elects to allow separate trading earlier, subject to the Company's (i) filing of a Current Report on Form 8-K with the Securities and Exchange Commission containing an audited balance sheet reflecting the Company's receipt of the gross proceeds of the Company's initial public offering and (ii) issuance of a press release announcing when such separate trading will begin. The terms of the Warrants are governed by a Warrant Agreement, dated as of                         , 2007, by and between the Company and Continental Stock Transfer & Trust Company, as Warrant Agent, and are subject to the terms and provisions contained therein, all of which terms and provisions the holder of this certificate consents to by acceptance hereof. Copies of the Warrant Agreement are on file at the office of the Warrant Agent at 17 Battery Place, New York, New York 10004, and are available to any Warrant holder on written request and without cost.

This certificate is not valid unless countersigned by the Transfer Agent and Registrar of the Company.

Witness the facsimile seal of the Company and the facsimile signatures of its duly authorized officers.

Prospect Acquisition Corp.

        The Company will furnish without charge to each stockholder who so requests, a statement of the powers, designations, preferences and relative, participating, optional or other special rights of each class of stock or series thereof of the Company and the qualifications, limitations, or restrictions of such preferences and/or rights. This certificate and the Units represented hereby are issued and shall be held subject to the terms and conditions applicable to the securities underlying and comprising the Units.

        The following abbreviations, when used in the inscription on the face of this certificate, shall be construed as though they were written out in full according to applicable laws or regulations:

Additional abbreviations may also be used though not in the above list.

For value received,                        hereby sells, assigns and transfers unto                        

                        Units represented by the within Certificate, and do hereby irrevocably constitute and appoint                        Attorney to transfer said Units on the books of the within named Company with full power of substitution in the premises.

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