Breakdown: Same-Sex Marriage in the U.S.

The hot-button social issue of same-sex marriage is widely expected to come before the United States Supreme Court once more as the court opens its new session.

The following are facts about same-sex marriage in the United States:

At the federal level:

-- The Supreme Court last June struck down parts of the Defense of Marriage Act (DOMA), which defined marriages as unions between "a man and a woman."

-- Legally married same-sex couples are now entitled to the same federal rights granted to their heterosexual counterparts.

States where same-sex marriage is legal:

-- Nineteen states, the U.S. capital, and 10 Native American tribes now recognize same-sex marriage either by law or constitution.

-- Most of the 19 are clustered around the northeastern United States: Massachusetts, Connecticut, Vermont, New Hampshire, New York, Iowa, and the capital Washington.

-- Maine, Maryland and Washington decided the issue by referendum in 2012; Rhode Island, Delaware and Minnesota followed suit in May 2013, shortly before the Supreme Court's historic ruling.

-- Following the Supreme Court ruling which gave the greenlight to California, other states have swung into line including New Jersey, Illinois, Hawaii, New Mexico, Oregon and Pennsylvania.

States where same-sex marriage is illegal:

-- In 31 states and two territories (Puerto Rico and Virgin Islands), same-sex marriage is explicitly forbidden in their constitution and legal framework. Most of the states are concentrated in southern, conservative regions.

-- The situation is frozen in 14 of them pending a court decision. The Supreme Court suspended same-sex marriages in Utah and Virginia.

-- In absence of same-sex marriage, eight states authorize civil unions which grant the same rights to same-sex couples as married heterosexuals.