The first same-sex weddings have taken place after gay marriage became legal in England and Wales at midnight.
Politicians from the main parties have hailed the change in the law.
David Cameron said the move sent a message that people were now equal "whether gay or straight", but some religious groups remain opposed.
Scotland passed a similar law in February; the first same-sex marriages are expected there in October. Northern Ireland has no plans to follow suit.
In an article for the Pink News website, the prime minister wrote: "This weekend is an important moment for our country.
"It says we are a country that will continue to honour its proud traditions of respect, tolerance and equal worth."
The law change would encourage young people unsure of their sexuality, he added.
Married at last
Married at last
“If you trust in yourself, and believe in your dreams, and follow your star. . . you'll still get beaten by people who spent their time working hard and learning things and weren't so lazy.”