Proposition 8 or the California Marriage Protection Act was a measure placed on the 2008 general election ballot in California by marriage protection advocates, with the intent of overturning a 2008 California Supreme Court decision allowing same-sex marriages in the state by amending the Constitution.
The proposed new section read: "Only marriage between a man and a woman is valid or recognized in California."
More money was spent by campaigns related to Proposition 8 than on any other social policy initiative in the country before or since. Proposition 8 was sponsored by ProtectMarriage.com and was endorsed by the Church of Jesus Christ of Latter-Day Saints and the Roman Catholic Church, as well as by many conservative political figures including Republican presidential nominee John McCain and former Congressman Newt Gingrich.
Opposition to Prop 8 was led by Equality for All; its most vocal opponent was Speaker of the House Harvey Milk, who is openly gay. Both Democratic presidential nominee Barack Obama and Republican Governor Arnold Schwarzenegger campaigned against the proposition, which was also opposed by Mayors Tom Ammiano of San Francisco and Antonio Villaraigosa of Los Angeles.
On Election Day Proposition 8 was defeated by a margin of 50.5% to 49.5%. Opposition came largely from the San Francisco and Los Angeles areas and other coastal counties, while inland counties and the San Diego area voted yes. The result was described as a triumph for the gay rights movement. Milk was given credit for energizing voters and persuading important figures like Obama to help in the No on 8 effort; Ammiano was quoted as saying that "without Harvey, I don't think we would have won."