A U.S. appeals court ruled on Tuesday that California's ban on same-sex marriage was unconstitutional.

Same-sex marriage is illegal in the vast majority of U.S. states, while only six -- New York, Connecticut, Massachusetts, Iowa, New Hampshire, Vermont -- and the District of Columbia allow it. California will make seven, although the ruling is on hold while proponents of the ban prepare an appeal. Where same-sex marriage is legal, it has been due to court rulings and legislative action , since popular votes have consistently backed bans.

Here is a timeline of laws on gay marriage in the United States:

* November 18, 2003 - Massachusetts' top court ruled that same-sex couples had the right to marry. The first legal same-sex marriages in the United States took place in Massachusetts in 2004 following the decision .

In 2008, Democrat governor Deval Patrick signed a law that allowed out-of-state same-sex couples to marry in Massachusetts , repealing a 1913 law that banned marriages not considered valid in the couples' home states.

* Oct. 10, 2008 - Connecticut legalized gay marriage, when its high court overturned a ban on same-sex marriage. Local authorities began issuing marriage licenses in November.

* Nov.4, 2008 - California joined the vast majority of U.S. states in outlawing same-sex marriage in 2008, when voters passed the ban known as Proposition 8. This overturned the California Supreme Court ruling in May 2008, that ruling that gender restrictions on marriage violate state equal rights protections.

In October 2009, Governor Arnold Schwarzenegger signed a bill that recognizes same-sex marriages performed in other states that went into effect on January 1, 2011.

* April 3, 2009 - Iowa's Supreme Court issued a unanimous ruling that said a gay marriage ban violated the constitutional rights of gay and lesbian couples. The state's first legal same-sex weddings took place later that month.

* April 7, 2009 - Vermont lawmakers overrode a governor's veto of a gay-marriage bill, making the New England state the first in the country to legalize gay marriage with a legislative vote. Its law took effect on Sept. 1 that year.

* June 3, 2009 - New Hampshire authorized same-sex nuptials after its Democratic-controlled House of Representatives endorsed gay marriage, hours after the state Senate approved the legislation along party lines. Governor John Lynch, a Democrat, signed the bill, which went into effect on Jan. 1, 2011.

* Nov. 4, 2009 - Maine's law permitting same-sex marriage was repealed by a people's veto. The law was approved by Maine's Legislature but was not implemented after it was overturned by a popular vote.

* December 15, 2009 - The District of Columbia's City Council voted to legalize same-sex marriage in the region. This came after the council voted in early 2009 to recognize same-sex marriages performed in other states where those unions were legal.

* August 4, 2010 - A federal judge in California struck down the state's ban on same-sex marriage as unconstitutional.

* June 24, 2011 - New York became the sixth U.S. state to allow gay marriage. After Democratic Governor Andrew Cuomo signed the law, gay couples rushed to make wedding plans. More than 21,000 gay and lesbian couples from New York would marry within the first three years, according to a report by the Independent Democratic Conference.

* Feb. 2, 2012- The Washington state Senate passed legislation to legalize gay marriage on Feb. 2. The bill is now before the state's House of Representatives, where it is expected to win swift approval.

* Feb. 7, 2012 - A U.S. appeals court ruled that California's gay marriage ban violates the constitution in a case that is likely to lead to a showdown on the issue in the Supreme Court.