North Carolina became the 30th state to ban same-sex weddings in the US hours before President Barack Obama finally voiced his support for gay marriage.
It is one of the most explosive social issues in American life, and has deeply divided public opinion and legislative efforts.
The uneven pattern across the nation of where gay marriage is legal and where it is not has been determined in large part by the 1996 Defense of Marriage Act which was signed into law by then president Bill Clinton.
The act left it up to each of the nation's 50 states to decide for themselves whether to legalize gay marriage or not, while stating that under federal law, marriage was "the union between a man and a woman."
So gay marriage is only recognized at the state level.
Since 2004, six states have legalized same-sex marriage: Connecticut, Iowa, Massachusetts, New Hampshire, New York and Vermont, along with the US capital, Washington, DC.
The states of Washington and Maryland have also voted in favor, but it has not yet come into effect due to pending referendums.
In California, same-sex marriages were allowed for about four and a half months in 2008, when thousands of couples flocked to say their vows, among them several notable celebrities.
But a series of legal challenges reversed the decision and has left the legal status of those couples in limbo.
Gay marriage was also approved in New Jersey, but the Republican governor opposed it with his veto. Gay rights groups are also planning a referendum in November in Maine.
Eight other states recognize same-sex civil unions.
According to a poll by the Pew Research Institute at the end of April, opinion has gradually swung in favor of gay marriage in the past decade. In 2001, 60 percent of people were against it compared with 43 percent today, with 35 percent in favor then compared with 47 percent in 2012.
According to the latest Gallup poll published on Tuesday, 50 percent of Americans think same-sex marriage should be legal in the United States, compared with 43 percent against.
But voters in southern North Carolina Tuesday approved a state constitutional amendment forbidding gay marriages, civil unions and domestic partnerships by 61 percent to 39 percent.
On the flip-side, states are increasingly having to grapple with the issue of divorce for same-sex couples who have married -- an issue which is now before the courts in some states such as Maryland.