In California's June 2000 primary, 61 percent of the electorate voted "yes" on Proposition 22, a measure that amended state law to read, "Only marriage between a man and a woman is valid or recognized " in the state. The state Supreme Court overturned the law in 2008 as discriminatory, opening the way for same-sex couples to get legally married in the state. About 18,000 gay and lesbian couples took advantage of the chance to tie the knot.

But the door that had been opened to same-sex couples slammed shut in November 2008, when voters passed Proposition 8. The measure, a constitutional amendment banning same-sex marriage, passed with 52 percent of the vote.

Gay-marriage advocates immediately filed challenges with the California Supreme Court, which agreed to hear the case, and in May 2009, the court upheld Prop. 8, another blow against same-sex marriage.