The European Union (EU) and Britain started the negotiations for a new partnership here on Monday.
The talks began with a bilateral meeting between the chief negotiators, the EU's Michel Barnier and the UK's David Frost, according to the audiovisual service website of the European Commission.
With around 100 British officials participating, the first round of negotiations will cover 11 areas including trade in goods and services, energy and transport, as the agenda showed on the UK government's website.
"We approach these negotiations in a constructive spirit. We want to agree an ambitious and fair partnership. We will respect our prior joint commitments," said Barnier on Twitter.
The first round of negotiations is set to last until Thursday.