What's at stake: The 1996 federal Defense of Marriage Act, which defines marriage as a union between a man and a woman, is being challenged. The law also prevents the federal government from recognizing same-sex marriages.
State action: Since 1996, many states have instituted their own bans on gay marriage, while eight states have approved it: Connecticut, New York, Iowa, Massachusetts, New Hampshire, Vermont, Maryland, Washington and the District of Columbia.
Federal action: President Obama said last year that the Department of Justice would no longer defend the law. After that, House Speaker John Boehner convened the Bipartisan Legal Advisory Group to defend it.
What's next: The 1st Circuit Court of Appeals is expected to issue its ruling within the next few months. The losing side is expected to appeal the issue to the Supreme Court later this year.