The most immediate battle ahead will be in November, when Californians are likely to get the chance to vote on an initiative that would effectively reverse the court ruling. Sponsors of a state constitutional amendment banning same-sex marriage have gathered more than 1.1 million signatures – enough to put it on the ballot.
Californians have split nearly evenly for years on the question. In June 2007, 45 percent favored allowing gay marriage and 49 percent opposed it, according to the Public Policy Institute of California (PPIC).
"Democrats are strongly in favor, Republicans are strongly opposed. It's a very sharp political divide on this question," says Mark Baldassare, PPIC president.
The case arose from San Francisco Mayor Gavin Newsom's instruction to the city clerk in 2004 to issue marriage licenses for same-sex couples. In the month that followed, nearly 4,000 same-sex couples got married before California's high court stepped in to halt the marriages and ultimately nullify them.
That brought lawsuits from some of the couples. The trial court found that codes barring same-sex marriages violated equal protection guarantees in the state's constitution. An appeals court reversed the decision, saying legal discrimination could be avoided through domestic partnership arrangements.
Writing for the majority in Thursday's ruling, Chief Justice Ron George found "that retention of the traditional definition of marriage does not constitute a state interest sufficiently compelling, under the strict scrutiny equal protection standard, to justify withholding that status from same-sex couples."