Gay marriage is one of the most polarising issues in the United States. Here we outline the state of the law across the country, and look at the often intense debates which have surrounded the issue.
In November 2006, Arizona voters rejected an amendment to the state constitution that would have banned domestic partnership laws as well as gay marriage.
It became the first state to reject such an amendment. Seven other states approved constitutional amendments banning gay marriage on the same day.
Arizona already had an ordinary law banning gay marriage, which remains in force.
California - America's most populous state - has the country's most colourful record on gay marriages.
The city of San Francisco started issuing marriage licences to same-sex couples in February 2004, after the city's new mayor decided to defy state law and allow gay weddings.
More than 3,400 gay couples got married before California's Supreme Court ordered a halt the following month.
During the wedding spree, gay couples flocked to California from across the US. But the weddings angered conservative groups, which launched legal challenges to ban the weddings.
California Governor Arnold Schwarzenegger came out against gay marriages, and told the state's attorney general to get a court ruling against them.
In August 2004, the state's Supreme Court ruled the mayor had exceeded his authority and nullified the unions.
But in a landmark decision on 14 March 2005, a judge ruled that California state law had breached a constitutional right to equal treatment of all citizens, irrespective of sexuality. That case has been appealed to a higher court and is expected to reach the state Supreme Court.
In September 2005, the state assembly became the first state legislature in the US to pass a bill endorsing gay marriages, following a similar move from the state Senate. Mr Schwarzenegger vetoed the bill.
California does allow same-sex couples to register as domestic partners, giving them many of the same rights under state law as married couples. Initially signed into law in 1999, the legislation has been repeatedly expanded and is similar in scope to the civil unions offered in some other states.
In April 2005, Connecticut became the first state in the country to create a legal framework for civil partnerships without being instructed to do so by a court. (Vermont had done so earlier after its Supreme Court ruled that refusing to do so was discrimination.)
Like Vermont, Connecticut bans gay marriage while allowing civil partnerships that confer many, but not all, of the same rights.
District of Columbia
Gay couples living in the District of Columbia can register as domestic partners.
The legislation gives them certain rights to visit their partner in hospital, make decisions about their partner's funeral arrangements and access to certain benefits.
State lawmakers in Hawaii in 1997 passed legislation allowing same-sex couples to enter into what the state calls a reciprocal beneficiary relationship.
The law grants limited rights, some of which are to do with health care decisions, inheritance without a will and hospital visitation.
Homosexual couples living in Maine have been able to register for domestic partnerships since July 2004.
The legislation grants registered couples rights to do with inheritance and funeral arrangements and explicit protection under domestic violence laws, but is more limited than the civil unions offered in some other states.
Massachusetts became the first state to issue marriage licences for gay couples, in May 2004, and weddings took place soon after, despite last-ditch legal attempts by conservative groups to halt the process.
This followed re-affirmation in February 2004 by the state's Supreme Court of a landmark ruling that it is a violation of the state constitution to ban gay marriage.
It had originally ruled on the issue as a result of a lawsuit filed in 2001 by seven gay couples, who sued the Massachusetts Department of Public Health after they were refused marriage licences.
State legislators later proposed a constitutional amendment that would ban gay marriages, but would allow civil unions, but the measure was effectively killed when the state house decided in November 2006 to recess rather than vote on it.
Lawmakers in New Hampshire approved same-sex civil unions in April 2007.
The bill, which gives legal recognition to gay partnerships, was passed by a 14-10 vote in the Democratic-held state senate. It was signed into law by Governor John Lynch on 31 May 2007 and comes into force on 1 January 2008.
The move was welcomed by Bishop Gene Robinson - the Episcopal Church's first openly gay bishop.
He told the Associated Press he and his partner wanted to be among the first gay couples in New Hampshire to officially unite under the civil unions law.
In December 2006, New Jersey lawmakers approved same-sex civil unions giving gay and lesbian couples the same rights as heterosexual couples.
Under the ruling, which came into effect in February 2007, gay couples gain benefits like adoption rights and inheritance rights. But the bill does not allow the unions to be called marriages.
The move came in response to the state's Supreme Court ruling in October 2006 that gay couples were entitled to the same rights as heterosexual couples. Seven gay couples had brought a case claiming that the state's constitution entitled them to marry.
The court ruled that they were entitled to the same rights as heterosexual couples and gave lawmakers six months to review the law. But it said it could not "find that the right to same-sex marriage is a fundamental right under our constitution".
The state has a tradition of expanding civil rights, having authorised domestic partnerships in 2004.
Officials in Sandoval County, New Mexico, issued marriage licences to gay couples for a matter of hours on 20 February 2004, following the lead of San Francisco.
More than 60 couples are believed to have been married before the state's attorney general ordered that they be stopped.
"No county clerk should issue a marriage licence to same-sex couples because those licences would be invalid under current law," New Mexico attorney general Patricia Madrid wrote in an "advisory" statement to local officials.
New Mexico's state legislature has considered a constitutional amendment limiting marriage to one man and one woman, but the measure died in committee, leaving state law silent on gay marriage.
New York's highest court, the Court of Appeals, ruled in July 2006 that the state constitution did not require New York to recognise gay marriages.
But New York is one of few US states that does not have a law on the book explicitly banning them, and the high court said the legislature could introduce same-sex marriage if it wished.
Gay-marriage advocates are thought to have little chance of getting such a law approved, a possible reason they took the case to the courts instead of the legislature.
Multnomah Country - which includes the city of Portland and is the most populous in Oregon - began issuing same-sex marriage licences on 3 March 2004.
About 3,000 were issued and another county, Benton, planned to follow suit.
But a judge ordered a freeze pending a court decision on the issue.
In November 2004, Oregon - along with 10 other states - voted to reject same-sex marriage.
In April 2005, the state's Supreme Court annulled the marriage licences issued in Multnomah County, saying they contravened state law.
Legislation to allow domestic partnerships in Oregon was signed into state law in May 2007. It offers same-sex partners many of the rights given to married couples under state law.
It is due to take effect on 1 January 2008 but could be delayed if opponents gather enough signatures to require a ballot of voters on the legislation.
In 2000, under the governorship of former Democratic presidential candidate Howard Dean, Vermont became the first US state to offer homosexuals the right to join in civil unions - although state law prevents them from being called marriages.
Under the legislation, same-sex partners resident in the state are allowed to apply for a licence similar to a marriage certificate, giving them the same benefits as married couples on matters such as life insurance, health care and child custody.
Couples wishing to separate have to go to court.
While the law grants homosexual couples many of the same rights as married people, the partnership is not recognised at the federal level.
President George W Bush has made clear that while he will support a constitutional amendment outlawing gay marriage, individual states like Vermont will still be able to make their own arrangements on unions.
A number of states have, however, already moved to outlaw not just gay marriage but also the Vermont-style civil union.
Since 22 July 2007, same-sex couples in the west coast state of Washington have been able to register as domestic partners.
The legislation gives them some of the rights and responsibilities afforded to married couples but is not as far-reaching as that of some other states which offer civil unions.
Last year Washington's Supreme Court upheld a ban on same-sex marriage passed by the state's lawmakers.