Marriage for all? The Supreme Court is considering whether all 50 states must allow same-sex marriage.

• Author: Smith, Patricia
• Position: NATIONAL

By this summer, Americans may know once and for all whether same-sex marriage is a right protected under the Constitution.

Same-sex marriage remains a politically divisive issue, even as many states have legalized it and courts have overturned bans approved by voters. Federal courts are in disagreement over the issue; some say yes, some say no. That's why the Supreme Court has decided to weigh in.

A year ago, same-sex marriage was legal in only 17 states. It's now legal in 36 of the 50 states and the District of Columbia (see maps). That means that more than 70 percent of Americans live in places where gay couples can wed.

"The landscape for marriage equality is changing lightning fast," says Suzanne Goldberg, a law professor at Columbia University in New York. "It is rare in American history that any civil rights change has moved as quickly as this."

If the Supreme Court does legalize same-sex marriage nationwide, it would be its most significant ruling on marriage since it struck down state bans on interracial marriage, in Loving v. Virginia, in 1967.

Proponents of same-sex marriage see it as a civil rights issue: Gay people, they argue, should have the same right to marry as everyone else, especially since many legal rights and family protections are tied to marriage. Opponents say allowing same-sex couples to marry undermines the institution of marriage, which many see as a religious rite going back thousands of years. They also object to courts overturning voter-approved bans.

"There is nothing in the Constitution that empowers the courts to silence the people and impose a nationwide redefinition of marriage," says Tony Perkins of the Family Research Council, a conservative policy group.

State laws regarding same-sex marriage have come about in three different ways: In some states, the courts have mandated the legalization of same-sex marriage. In others, the state legislature has legalized it. Finally, there are state referendums, in which voters have banned gay marriage. Almost all those bans have been challenged in court, and some have been overturned.

The Supreme Court has already given same-sex-marriage advocates a partial victory. In 2013, in United States v. Windsor, the Court overturned the federal Defense of Marriage Act. That 1996 law barred the federal government from giving benefits tied to marriage, such as tax breaks, to same-sex couples.

But the Windsor ruling didn't address whether state bans on gay marriage were...