California becomes the second U.S. state after Massachusetts in 2004 to legalize same-sex marriage after the state's own Supreme Court rules a previous ban unconstitutional.

Same-sex marriage has been legal in California since June 28, 2013. The State of California first issued marriage licenses to same-sex couples from June 16, 2008 to November 5, 2008, as a result of the Supreme Court of California finding in the case of In re Marriage Cases that barring same-sex couples from marriage violated the Constitution of California. The issuance of such licenses was halted from November 5, 2008 through June 27, 2013 due to the passage of Proposition 8—a state constitutional amendment barring same-sex marriages. The granting of same-sex marriages resumed following the U.S. Supreme Court's decision in Hollingsworth v. Perry, which restored the effect of a federal district court ruling that overturned Proposition 8 as unconstitutional.

In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sovereignty with the federal government. Due to this shared sovereignty, Americans are citizens both of the federal republic and of the state in which they reside. State citizenship and residency are flexible, and no government approval is required to move between states, except for persons restricted by certain types of court orders.

Same-sex marriage has been legally recognized in Massachusetts since May 17, 2004, as a result of the Massachusetts Supreme Judicial Court (SJC) ruling in Goodridge v. Department of Public Health that it was unconstitutional under the Constitution of Massachusetts to allow only opposite-sex couples to marry. Massachusetts was the sixth jurisdiction in the world to legalize same-sex marriage after the Netherlands, Belgium, Ontario, British Columbia, and Quebec. It was the first U.S. state to open marriage to same-sex couples.