FACTBOX: U.S. laws on gay marriage, civil unions

(Reuters) - The following is a look at laws on gay marriage and same-sex civil unions in the United States after a vote by lawmakers in Vermont on Tuesday that will make the New England state the fourth in the nation to allow gay marriage.

* 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 April 3 that said the state's same-sex marriage ban violated the constitutional rights of gay and lesbian couples.

* Vermont lawmakers on Tuesday overrode a veto from the governor of a bill that would allow same-sex marriage, making the tiny New England state the first in the country to legalize gay marriage with a Legislature's vote.

* New Hampshire and New Jersey 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.

* Forty-three U.S. states have laws explicitly prohibiting such marriages, including 29 with constitutional amendments restricting marriage to one man and one woman.

* 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)