The US Supreme Court has ruled that same-sex marriage is a legal right across the United States.
It means the 14 states with bans on same-sex marriage will no longer be able to enforce them.
Justice Anthony Kennedy wrote that the plaintiffs asked "for equal dignity in the eyes of the law. The Constitution grants them that right."
The ruling brings to an end more than a decade of bitter legal battles.
Same-sex couples in several affected states including Georgia, Michigan, Ohio and Texas rushed to wed on Friday.
However officials in other states, including Mississippi and Louisiana, said marriages had to wait until procedural issues were addressed.
President Barack Obama said the ruling was a "victory for America".
"When all Americans are treated as equal, we are all more free " he said.
However, Christian conservatives condemned the decision.
Former Arkansas governor and presidential candidate Mike Huckabee called it "an out-of-control act of unconstitutional, judicial tyranny".
And Kellie Fiedorek, a lawyer for an anti-gay marriage advocacy group, said the decision "ignored the voices of thousands of Americans".
Greg Abbott, the governor of Texas, a state where marriages licences will now be issued to same-sex couples, said the justices "have imposed on the entire country their personal views on an issue that the Constitution and the Court's previous decisions reserve to the people of the states".
At the scene - Paul Blake, BBC News
Loud cheers erupted outside the court after the ruling was announced, and there were tears, hugs, and cheers of "USA USA USA!".
A sea of rainbow flags overwhelmed the few anti-gay marriage activists who reacted in disbelief, and the demonstration seemed to turn into a street party.
A tour bus drove past honking as hundreds cheered the decision.
One of the demonstrators, Jordan Monaghan, called his mother from his mobile phone amid the celebrations.
"Hey mom, I'm at the Supreme Court. Your son can have a husband now," Mr Monaghan said.
Minutes after the ruling, couples in one of the states that had a ban, Georgia, lined up in hope of being wed.
In Texas, Yasmin Menchaca and her partner Catherine Andrews told the BBC that they are "trying to round up our parents" in order to get married on Friday.
The two have been together for six years, and had attempted to marry in Washington state - but decided to wait because of the financial burden of flying their parents across the country.
On social media, Democratic presidential candidate Hillary Clinton merely tweeted the word "proud" and the White House changed its Twitter avatar into the rainbow colours.
The case considered by the court concerned Jim Obergefell, an Ohio resident who was not recognised as the legal widower of his late husband, John Arthur.
"It's my hope that gay marriage will soon be a thing of the past, and from this day forward it will simply be 'marriage,'" an emotional Mr Obergefell said outside the court.
- Alabama, Arkansas, Georgia, Kentucky, Louisiana, Michigan, Mississippi, most of Missouri, Nebraska, North Dakota, Ohio, South Dakota, Tennessee and Texas.
The first state to allow same-sex marriage was Massachusetts, which granted the right in 2004.
In recent years, a wave of legal rulings and a dramatic shift in public opinion have expanded gay marriage in the US.
In 2012, the high court struck down a federal anti same-sex marriage law.