The first round of formal talks on Britain's withdrawal from the European Union has begun in Brussels.
Brexit Secretary David Davis said: "We are starting this negotiation in a positive and constructive tone, determined to build a strong and special partnership between ourselves and our European allies and friends for the future."
Speaking at a joint news conference, the European Commission’s Chief Negotiator Michel Barnier said: "Our objective is clear, we must first tackle the uncertainties caused by Brexit.
"First for citizens, but also for the beneficiaries of the EU policies and for the impacts on borders, in particular Ireland."
Mr Barnier added that he hoped on the first day of talks "we can identify priorities and a timetable".
He added: "That will also me to report to the European Council later this week that we had a constructive opening for negotiations."
Senior officials from the Home Office and Treasury joined Mr Davis at the negotiating table.
They included Olly Robbins, the senior civil servant at the Department for Exiting the European Union, and Sir Tim Barrow, the UK's ambassador to the EU.
Mr Barnier was backed by a 10-strong team for the talks, with his deputy Sabine Weyand by his side.
Former French minister Mr Barnier has previously said the UK will have less than 18 months to negotiate and any deal must be finalised by October 2018.
Despite the initial optimism, negotiations are likely complex as officials get to grips with untangling a relationship that goes back 40 years and covers a host of issues and laws.
The UK wants to begin working out the details of a trade agreement alongside the terms of the withdrawal process.
However, Europe says that an agreement on issues such as the rights of citizens, the divorce bill and border controls must come before considering any post-Brexit settlement.