Same-sex marriage law in the United States by state in the context of Domestic partnerships

The legal recognition of same-sex marriage in the United States expanded from one state in 2004 (Massachusetts) to all 50 states in 2015 through various court rulings, state legislation, and direct popular vote. States have separate marriage laws, which must adhere to rulings by the Supreme Court of the United States that recognize marriage as a fundamental right guaranteed by both the Due Process Clause and the Equal Protection Clause of the Fourteenth Amendment to the United States Constitution, as first established in the 1967 landmark civil rights case of Loving v. Virginia. Same-sex marriages are also licensed in and recognized by Washington, D.C. and all U.S. territories except for American Samoa, but not in some Native American tribal nations.

Civil rights campaigning in support of marriage without distinction as to sex or sexual orientation began in the 1970s. In 1972, the later-overturned Baker v. Nelson saw the Supreme Court of the United States decline to become involved. The issue became prominent from around 1993, when the Supreme Court of Hawaii ruled in Baehr v. Lewin that it was unconstitutional under the Constitution of Hawaii for the state to abridge marriage on the basis of sex. That ruling led to federal and state actions to explicitly abridge marriage on the basis of sex in order to prevent the marriages of same-sex couples from being recognized by law, the most prominent of which was the 1996 federal Defense of Marriage Act (DOMA). In 2003, the Massachusetts Supreme Judicial Court ruled in Goodridge v. Department of Public Health that it was unconstitutional under the Constitution of Massachusetts for the state to abridge marriage on the basis of sex. From 2004 through to 2015, as the tide of public opinion continued to move towards support of same-sex marriage, various state court rulings, state legislation, direct popular votes (referendums and initiatives), and federal court rulings established same-sex marriage in thirty-six of the fifty states.