The Supreme Court announced on Friday that it will decide two major gay marriage cases next year that could have a sweeping effect on the rights of same-sex couples to wed. The cases, which likely won't be decided until June, mark the first time the justices will consider arguments for and against same-sex marriage.

The court will review California's gay marriage ban, which passed in a 2008 ballot initiative months after California's high court had legalized same-sex unions and thousands of gay Californians had already tied the knot. Two federal courts have struck down Proposition 8 as discriminatory, leaving the Supreme Court to render a final judgment.

The justices will also hear a challenge to the federal Defense of Marriage Act, a law passed under President Bill Clinton that prevents the federal government from recognizing gay marriages. Windsor v. United States was brought by Edith Windsor, a resident of New York who paid $363,000 in estate taxes after her wife died because the federal government did not recognize their marriage. New York is one of nine states (and the District of Columbia) where gay marriage is legal, so Windsor argues that the federal government is discriminating against her by not recognizing her state-sanctioned marriage.

The Obama administration decided last year to no longer defend DOMA, so Congress has hired outside counsel to argue on behalf of the law. Recently, two federal appeals courts had struck down the law as unconstitutional, virtually requiring the Supreme Court to take the case to settle the dispute between the courts and Congress.

Legal experts are skeptical that the court would deliver a sweeping ruling deciding whether all Americans, regardless of sexual orientation, have a fundamental right to marry in the DOMA case. It's more likely they will narrowly decide whether the federal government has a legitimate interest in refusing to recognize same-sex couples who wed in states where gay marriage is legal. (Marriage has traditionally been regulated by the states.)

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In the Proposition 8 case, justices may decide whether a ban on gay marriage is legal in the specific case of California, where gay couples were allowed to marry for several months before the ban passed. Such a narrow decision would not necessarily affect gay marriage bans that have passed in dozens of other states where same-sex marriage was never legal in the first place.

But it's possible the justices could make a broader ruling on Prop 8. Ted Olson, a former U.S. solicitor general under President George W. Bush and one of the lead attorneys in the battle against Proposition 8, told reporters on Friday that he planned to argue that there's a "fundamental constitutional right to marry for all citizens." His co-counsel, David Boies, called same-sex marriage the civil rights issue of this era. If the justices accept this argument, states could no longer ban gay marriage, dealing the anti-gay marriage movement a fatal blow. If they reject the argument, it would shut down legal challenges to state marriage bans and significantly set back the movement to expand same-sex marriage rights.

John Eastman, the chair for the anti-gay marriage National Organization for Marriage, said in a statement that he thinks the Supreme Court will uphold Proposition 8 and DOMA. "We believe the U.S. Supreme Court will overturn this exercise in judicial activism and stop federal judges from legislating from the bench on the definition of marriage," Eastman said.

For both cases, court-watchers will have their eyes trained firmly on swing Justice Anthony Kennedy, who has a record of ruling in favor of gay rights. In 2003, Kennedy wrote the court's opinion in Lawrence v. Texas, a landmark decision that said the government cannot outlaw anal sex between consenting adults, whatever their sexual orientation. ("The liberty protected by the Constitution allows homosexual persons the right to choose to enter upon relationships in the confines of their homes and their own private lives and still retain their dignity as free persons," he wrote.) Kennedy also wrote the majority opinion striking down a Colorado law that would have prevented local governments from passing laws specifically protecting gay civil rights.

Because of Kennedy's history on the issue, many legal experts think there's a good chance the court will strike down DOMA, with Kennedy joining the court's four liberals for the decision. But the workings of the Supreme Court are notoriously hard to predict, and it's still a complete mystery what the nine justices will decide in June.