EXHIBIT 5.1

                              Goodwin Procter LLP
                               Counsellors at Law
                                 Exchange Place
                             Boston, MA 02109-2881
                               T: (617) 570-1057
                               F: (617) 523-1231

                                 March 29, 2001

AvalonBay Communities, Inc.
2900 Eisenhower Avenue, Suite 300
Alexandria, VA 22314

    Re:  Legality of Securities to be Registered
       under Registration Statement on Form S-3

Ladies and Gentlemen:

    This opinion is delivered in our capacity as counsel to AvalonBay
Communities, Inc., a Maryland corporation (the "Company"), in connection with
the Company's registration statement on Form S-3 (the "Registration Statement")
filed with the Securities and Exchange Commission under the Securities Act of
1933, as amended, which relates to the sale from time to time of an
indeterminate amount of debt securities ("Debt Securities"), shares of preferred
stock, par value $.01 per share ("Preferred Stock"), shares of common stock, par
value $.01 per share ("Common Stock"), and the rights (the "Rights") to purchase
shares of Series E Junior Participating Cumulative Preferred Stock, par value
$.01 per share, which are attached to all shares of Common Stock, or any
combination of Debt Securities, Preferred Stock and Common Stock and the
associated Rights (collectively, the "Securities"), having a maximum aggregate
public offering price of $750,000,000. The Registration Statement provides that
the Securities may be offered separately or together, in separate series, in
amounts, at prices and on terms to be set forth in one or more prospectus
supplements (each a "Prospectus Supplement") to the prospectus contained in the
Registration Statement.

    We have examined the charter of the Company, as amended and on file with the
Maryland State Department of Assessments and Taxation, the bylaws of the
Company, as amended, such records of corporate proceedings of the Company as we
have deemed appropriate for the purposes of this opinion, the Registration
Statement and the exhibits thereto.

    Based upon the foregoing, we are of the opinion that (i) when the Securities
are specifically authorized for issuance by the Company's Board of Directors or
an authorized committee thereof (the "Authorizing Resolution"), (ii) upon
receipt by the Company of the full consideration therefor as provided in the
Authorizing Resolution and (iii) upon the issuance of the Securities as
described in the Registration Statement and a Prospectus Supplement that is
consistent with the Authorizing Resolution, the Securities will be legally
issued, fully paid and nonassessable.

    We hereby consent to being named as counsel to the Company in the
Registration Statement, to the references therein to our firm under the caption
"Legal Matters" and to the inclusion of this opinion as an exhibit to the
Registration Statement.

                                            
                                               Very truly yours,

                                               /s/ GOODWIN PROCTER LLP
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                                               GOODWIN PROCTER LLP