Who should be allowed to marry? As more states legalize same-sex marriage, the issue may be headed back to the Supreme Court.

• Author: Smith, Patricia
• Position: NATIONAL

On June 1, Illinois will become the 17th state to legalize same-sex marriage. At that point, almost 40 percent of the country's population will live where it's legal for two men or two women to marry.

Just 10 years ago, there was only one state where it was legal: Massachusetts.

Same-sex marriage is still one of the most politically divisive issues in the nation. But in the courts and in the court of public opinion, the issue is moving so quickly that the Supreme Court may have to decide soon whether gay marriage is a right protected by the Constitution.

"It is rare in American history that any civil rights change has moved as quickly as this," says Suzanne Goldberg, a law professor at Columbia University in New York, adding that "pressure is building in society and building in the courts."

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.

"Marriage is about identifying that there is this one unique relationship in humankind--the union of a man and a woman," says Joe Grabowski of the National Organization for Marriage.

Seventeen states and the District of Columbia have legalized gay marriage since 2003. But 33 states have moved in the opposite direction with constitutional bans against gay marriage or laws prohibiting it (see map).

State laws regarding same-sex marriage have come about in three different ways: from the courts, state legislatures, and voters. In some states, like Massachusetts, the state Supreme Court mandated the legalization of same-sex marriage. In other states, like Vermont, legislatures passed laws legalizing it. Finally, there's the ballot measure route, in which voters have banned gay marriage, most often by amending state constitutions to define marriage as between a man and a woman. Almost all those bans have been challenged in court.

What the Courts Say

The Supreme Court has already given same-sex-marriage advocates a partial victory. Last June, in the case 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--including tax breaks and healthcare benefits for federal employees--to...