Background:In May 2008, California became the second state in the U.S. (after Massachusetts) to allow same-sex marriage. Anti-gay activists put a measure on the California ballot to change the constitution to make marriage only between a man and a woman. Prop 8 passed 52-48%. Gay and lesbian couples are no longer be allowed to marry in California.
Update:The California Supreme Court ruled on May 26, 2009 that Prop 8 will stand as law in California, but the marriages of the 18,000 or so same-sex couples who married between June and November 2008, before Prop 8 was passed will remain valid. But from this point on, same-sex marriages will not be legal in California.
Sources: No on 8, HRC, Los Angeles Times