From February 12 to March 11, 2004, under the direction of Mayor Gavin Newsom of San Francisco, officials of the City and County of San Francisco issued marriage licenses to approximately 4,000 same-sex couples despite it being illegal to do so at both the state and federal level. During the month that licenses were issued, couples traveled from all over the United States and from other countries to be married. On August 12, citing the Mayor's lack of authority to bypass state law, the Supreme Court of California ruled that the marriages were void. Consolidated lawsuits against the State Government in favor of same-sex marriage which followed eventually reached the Supreme Court of California. On May 15, 2008, it overturned the state's ban on same-sex marriage with the ruling In re Marriage Cases. The four-to-three decision took effect on June 16, 2008. Two weeks earlier, the initiative to override this result of the court decision qualified for the November election ballot. The Court declined to stay its decision until after the November elections. Some reports suggested that out-of-state same-sex couples would marry in California prior to the 2008 elections because California does not require the marriage to be valid in the couple's home state.
The ballot initiative, Proposition 8, a state constitutional amendment titled Eliminates Right of Same-Sex Couples to Marry Act, appeared on the California general election ballot in November 2008 and passed with a 52% majority. Support for Proposition 8 was not uncontroversial, with Mormons and the Mormon Church donating $20 million to campaign for its passage. As for the opposition, the California Supreme Court heard several challenges to Proposition 8 in March 2009, but ultimately upheld the amendment, though the over 18,000 couples that were married in the time before Prop 8 was passed remained valid.
California continues to allow domestic partnership. This grants same-sex couples almost all state-level rights and obligations of marriage but does not apply to "federal-level rights of marriage that cannot be granted by states." However, since June 2015, same sex marriages are recognized and performed, as well as recognized by the Federal Government. UCLA's Williams Institute on Sexual Orientation Law and Public Policy projected in June 2008 that about half of California's more than 100,000 same-sex couples would wed during the next three years and 68,000 out-of-state couples would travel to California to exchange vows.