A federal judge in San Francisco on Wednesday struck down California's ban on gay marriage, a ruling that, while it will likely be appealed all the way to the U.S. Supreme Court, hands a key victory to gay rights advocates.
The Supreme Court has not taken a case on gay marriage, leaving states to decide on the issue, although the California federal challenge is aimed at eventually reaching the country's top court.
Following is a look at laws on gay marriage and same-sex civil unions in the United States.
* Five states and the District of Columbia have approved gay marriage: Iowa, Connecticut, Massachusetts, New Hampshire and Vermont.
* Thirty-nine U.S. states have laws explicitly prohibiting such marriages, including 30 with constitutional amendments restricting marriage to heterosexual couples, according to DOMA Watch, an advocacy group that supports marriage between one man and one woman.
* Courts and state legislatures have legalized gay marriage in the United States but popular votes have consistently opposed same-sex marriage, most recently in Maine where voters repealed a law implemented by the state's legislature through a "people's veto."
* Arizona is the only state where voters rejected a constitutional ban on gay marriage in 2006 but approved a similar measure in 2008.
* The first legal same-sex marriages in the United States took place in Massachusetts in 2004. On July 8, a U.S. district court judge in the state ruled that a federal ban on same-sex marriage is unconstitutional, arguing that the 1996 Defense of Marriage Act interferes with the right of the states to define marriage.
* California, Oregon, New Jersey, Nevada and Washington offer gay couples the equivalent of state spousal rights but Colorado, Hawaii, Maine and Wisconsin only provide some spousal rights to same-sex partners, according to the Human Rights Campaign, a gay rights advocacy group.
* On July 6, Hawaii Governor Linda Lingle, a Republican, vetoed a bill that would have allowed same-sex couples to form civil unions, saying the bill would have created "marriage by another name."
(Compiled by Ros Krasny in Boston, Edith Honan in New York, Courtney Hoffman in San Francisco and Dan Whitcomb in Los Angeles; Editing by Cynthia Osterman)