1
                                                                     EXHIBIT 5.1



                         [LATHAM & WATKINS LETTERHEAD]



                                 August 9, 2000



Leap Wireless International, Inc.
10307 Pacific Center Court
San Diego, California  92121

               Re:    Registration Statement on Form S-3;
                      163,076 Shares of Common Stock, par value $.0001 per share

Ladies and Gentlemen:

               In connection with the registration under the Securities Act of
1933, as amended (the "Act"), of 163,076 shares (the "Shares") of common stock,
par value $.0001 per share, of Leap Wireless International, Inc., a Delaware
corporation (the "Company"), pursuant to a Registration Statement on Form S-3
filed with the Securities and Exchange Commission (the "Commission") on August
9, 2000 (the "Registration Statement") to register certain resales of the Shares
by the selling security holder named in the Registration Statement, you have
requested our opinion with respect to the matters set forth below.

               In our capacity as your counsel in connection with such
registration, we are familiar with the proceedings taken and proposed to be
taken by the Company in connection with the authorization, issuance and sale of
the Shares, and for the purposes of this opinion, have assumed such proceedings
will be timely completed in the manner presently proposed. In addition, we have
made such legal and factual examinations and inquiries, including an examination
of originals or copies certified or otherwise identified to our satisfaction of
such documents, corporate records and instruments, as we have deemed necessary
or appropriate for purposes of this opinion.

   2

LATHAM & WATKINS

Leap Wireless International, Inc.
August 9, 2000
Page 2


               In our examination, we have assumed the genuineness of all
signatures, the authenticity of all documents submitted to us as originals, and
the conformity to authentic original documents of all documents submitted to us
as copies.

               We are opining herein as to the effect on the subject transaction
only of the General Corporation Law of the State of Delaware, including
statutory and reported decisional law thereunder, and we express no opinion with
respect to the applicability thereto, or the effect thereon, of the laws of any
other jurisdiction or, in the case of Delaware, any other laws, or as to any
matters of municipal law or the laws of any local agencies within any state.

               Subject to the foregoing, it is our opinion that as of the date
of this opinion, the Shares have been duly authorized, validly issued and are
fully paid and nonassessable.

               We consent to your filing this opinion as an exhibit to the
Registration Statement and to the reference to our firm contained under the
heading "Legal Matters."

                                               Very truly yours,

                                               /S/ LATHAM & WATKINS