Same sex couples planning on getting married on the first day in which it becomes legal can register for their ceremony from today.
March 29th will see the first gay and lesbian marriages under the Marriage (Same Sex Couples) Act 2013, with registration opening today.
Couples getting hitched on the first day will not be the first married same sex couples however.
Anyone living in the UK who had their same sex marriage overseas will have it automatically legally recognised from today.
There is a slight delay, however, in advice for couples in a civil partnership to convert their arrangement into a marriage - with couples unlikely to hear how to 'upgrade' until the end of the year.
There is no compulsion for civil partners to 'upgrade' but many are expected to do so.
Some equalitycampaigners are still pushing the government to allow hetrosexual couples to have a civil union.
"The government's argument that heterosexual civil partnerships would cost too much is unseemly," human rights campaigner Peter Tatchell said.
"You can't put a price on equality.
"While I applaud David Cameron for standing firm on equal marriage rights for same-sex couples, I am shocked that he is opposing the right of heterosexual couples to have a civil partnership.
"He said he's supporting same-sex marriage because he believes in equality, yet he won’t support equal civil partnerships for opposite-sex couples. That's not consistent."
Religious organisation can 'opt-in' to conducting same sex marriage ceremonies, although the Church of England and Church of Wales are barred from doing so.
Cameron put down the exception at the height of the row over gay marriage.