“It affects every aspect of life,” Justice Ruth Bader Ginsburg said during oral argument.

The Government Accountability Office has identified more than 1,100 areas of federal law in which marriage matters, ranging from tax and welfare benefits to employment and immigration. Same-sex military couples, for instance, are denied housing, health insurance and disability benefits, and are ineligible for burial alongside their spouses in national cemeteries.

“The statute is invalid, for no legitimate purpose overcomes the purpose and effect to disparage and injure those whom the state, through its marriage laws, sought to protect in personhood and dignity,” Kennedy wrote.

Twelve states and the District of Columbia now recognize same-sex marriage, and a recent Pew Research Center survey found that 72 percent of those asked thought that legal recognition of gay marriage was inevitable.

While the decisions were read inside the court starting at 10 a.m. EDT, sparking a frantic rush by reporters to figure out what the justices had concluded, a large crowd outside anxiously checked iPhones and Androids for the latest updates.

Each case involved a separate set of facts and distinct legal reasoning.

PROPOSITION 8

The challenge was brought on behalf of several same-sex couples, including Kristin M. Perry and her partner, Sandra Stier, and Paul Katami and his partner, Jeffrey Zarrillo. Both couples were denied marriage licenses in California because of the Proposition 8 ban.

The California case arose after the state Supreme Court ruled that same-sex couples had the right to marry. Voters subsequently changed the state’s constitution in 2008, in the Proposition 8 ballot measure, to limit marriages to those between one man and one woman.

The Obama administration proposed that the court protect same-sex marriage specifically in the handful of states that ban it but accept gay civil unions. The justices, though, showed little interest in this proposal.

After a high-profile, 12-day trial in San Francisco, U.S. District Judge Vaughn Walker issued an unusually detailed, 136-page opinion in August 2010 in which he concluded that Proposition 8 violated the U.S. Constitution.

Walker retired in 2011, at which time he told reporters he was gay and in a long-standing relationship with another man. Conservative supporters of Proposition 8 failed in their subsequent attempt to claim that Walker was biased because of his sexuality.

The 9th U.S. Circuit Court of Appeals upheld Walker’s decision, though for a very state-specific reason that essentially confined its reach to California: The California Supreme Court had recognized same-sex marriage rights in May 2008, and then voters removed those rights in November 2008 by approving the ballot measure.

California state officials declined to defend the same-sex marriage ban. Instead, a conservative former Southern California state legislator named Dennis Hollingsworth and allies argued on the proposition’s behalf.

The California Supreme Court concluded, and the 9th Circuit Court of Appeals accepted the view, that the opponents were authorized to step in since the state had stepped out.

DEFENSE OF MARRIAGE ACT

The federal law defining marriage inserted the national government into what traditionally had been state territory.

The case arose from a challenge filed by Edith Windsor, a computer programmer who married her longtime partner, Thea Clara Spyer, in 2007. They remained a couple until Spyer died in 2009. The Defense of Marriage Act prohibited Windsor from receiving a deduction afforded married couples. She had to pay $363,053 in estate taxes, and the Internal Revenue Service denied her refund request.