Yesterday in New Jersey hundreds of gay couples were given the same rights as married straight couples, and hundreds have joined in civil unions in the first 24 hours.
Civil unions offer the same legal advantages as marriage, but not the title, and were given automatically to any same-sex couple who had already been married or joined in civil unions elsewhere.
Couples who had not been joined previously could apply for the licence, but have to wait 72 hours, the same waiting period for a wedding, until they can hold the ceremony.
The laws were put into place after a state Supreme Court ruling in October held that gay couples had the same rights as married couples.
But campaigners for gay marriage intend to sue, claiming that a civil union will not afford the same rights as marriage.
Meanwhile, conservative groups have sworn to fight this latest step in the move towards equality for gay people.
They are pressing for amendment to the state constitution which would ban civil unions.
Only one state, Massachusetts, has legislated marriage for same-sex couples, while three other American states (Connecticut, Vermont and California) allow civil unions or domestic partnerships.