In United States v. Windsor, 570 U.S.— (June 26, 2013) the U.S. Supreme Court struck down Section 3 of the Defense of Marriage Act (DOMA) defining “marriage” to mean “only a legal union between one man and one woman as husband and wife” under federal law. (1 U.S.C. §7.)

By treating legal same-sex marriages differently from opposite-sex ones, the court found, “DOMA’s principal effect is to identify a subset of state-sanctioned marriages and make them unequal,” thereby “writ[ing] inequality into the entire United States Code.” Such discrimination violates “the prohibition against denying to any person the equal protection of the laws.”