California Proposition 8 was a ballot initiative passed in November 2008 that aimed to define marriage as a union between one man and one woman. This measure effectively banned same-sex marriage in California, reversing the state Supreme Court's earlier decision that had legalized it. The proposition sparked significant public debate and led to widespread protests and legal challenges. In 2010, a federal court ruled that Proposition 8 was unconstitutional, and the case eventually reached the U.S. Supreme Court, which declined to hear the appeal, effectively allowing same-sex marriage to resume in California.