[From Summary] Massachusetts became the first state to legalize marriage between same-sex couples May 17, as a result of a November 2003 decision by the state's highest court that denying gay and lesbian couples the right to marry violated the state's constitution. Currently federal law does not recognize same-sex marriages. This report discusses the Defense of Marriage Act (DOMA), P.L. 104-199, which prohibits federal recognition of same-sex marriages and allows individual states to refuse to recognize such marriages performed in other states, as well as the potential legal challenges to the DOMA. Moreover this report summarizes the legal principles applied in determining the validity of a marriage contracted in another state; surveys the various approaches employed by states to prevent same-sex marriage; and discusses the recent House and Senate Resolutions introduced proposing a constitutional amendment (H.J.Res. 56, S.J.Res. 26, S.J.Res. 30, and S.J.Res. 40) and limiting Federal courts’ jurisdiction to hear or determine any question pertaining to the interpretation of DOMA. (H.R. 3313). On July 14, 2004, the Senate considered and voted on a required procedural motion. This motion failed by a vote of 48-50, which prevented further consideration of S.J.Res. 40. On July 22, 2004, the House voted on and passed H.R. 3313.