EU leaders have agreed to move Brexit talks on to the second phase, says European Council President Donald Tusk, the BBC reports.
This means talks can move on to the long-term relationship between the UK and EU, including trade and security.
The first issue to be discussed, as early as next week, will be the terms of a transition period after the UK leaves in March 2019.
European Commission President Jean-Claude Juncker has warned this process will be “significantly harder”.
Mr Tusk tweeted the news after a meeting of the other 27 EU leaders in Brussels.
— Donald Tusk (@eucopresident) December 15, 2017
He congratulated UK Prime Minister Theresa May on reaching what the BBC’s political editor Laura Kuenssberg said was a major moment in the Brexit process.