(Reuters) - The following is a look at laws on gay marriage and same-sex civil unions in the United States following an Iowa Supreme Court ruling on Friday that cleared the way for the state to become the third in the country to legalize same-sex weddings.
* Massachusetts' highest court ruled in 2003 that a ban on gay marriage was unconstitutional, paving the way for America's first same-sex marriages the following year.
* Connecticut's Supreme Court overturned a ban on same-sex marriage on October 10, 2008. Local authorities began issuing marriage licenses on November 12, making it the second state to allow gay and lesbian couples to marry.
* California began marrying gay and lesbian couples in June 2008, a month after the state Supreme Court ruled that barring same-sex marriages was unconstitutional. But that was reversed on November 4 when Californians voted in support of a proposition to amend the state constitution to ban same-sex marriage.
* Iowa's Supreme Court issued a unanimous ruling on Friday that said the state's same-sex marriage ban violated the constitutional rights of gay and lesbian couples.
* Iowa's ruling came a day after the Vermont House of Representatives passed a bill that would legalize gay marriage, but supporters failed to get enough votes to override a veto threat from the governor.
* New Hampshire, New Jersey and Vermont permit same-sex civil unions that grant largely the same state rights as married couples -- from insurance coverage to tax benefits and hospital visiting rights -- but lack the full legal protections of marriage.
* Maine, the District of Columbia, Hawaii and Washington each offer gay couples some legal rights as partners.
* Lawmakers in New Hampshire and Maine are currently considering bills to allow gay marriage.
* The patchwork of laws has caused some unusual complications. Rhode Island's top court, for example, ruled in December 2007 that a same-sex couple married in Massachusetts could not legally divorce in Rhode Island, saying the state's family court did not have authority over same-sex marriages.
* The U.S. Supreme Court has not taken a case on gay marriage, leaving states to decide the issue.
Compiled by Jason Szep in Boston, Editing by Frances Kerry