Almost exactly a year after Britain's seismic referendum to leave the bloc, the EU's chief negotiator, Michel Barnier of France, welcomed his counterpart David Davis with a cheery handshake at the European Commission in Brussels, AFP wrote.
The smiles belied the fact that at stake is not just Britain's future but also Europe's postwar political order and its place in the world, which could be fatally undermined without an agreement by the March 2019 deadline.
"We must first tackle the uncertainties caused by Brexit," Barnier said, citing the rights of EU citizens in Britain and the possible impact on the open border between Northern Ireland and Ireland.
"I hope today we can identify priorities and a timetable that would allow me to report to the European Council (summit) later this week that we had a constructive opening of negotiations," added the former European commissioner and French foreign minister, speaking against a backdrop of British and EU flags.
A key issue he did not mention was the EU's bill for Britain to leave, which Brussels estimates at a colossal 100 billion euros.
'Positive and constructive'
Davis, a prominent tough-talking figure in the "Leave" campaign, sounded a positive note, saying that while there would "undoubtedly be challenging times ahead" he wanted a good relationship with the EU.
European stocks rose on Monday, partly on optimism about the talks actually getting underway after months of sniping and uncertainty, analysts said.
In Berlin, German Chancellor Angela Merkel emphasized the unity of the remaining 27 EU countries, who have been alarmed in recent weeks by May's threats to walk out of the talks.
"I would like us to get a good agreement that is in both sides’ interests. But the 27 of us will formulate our interests very clearly and hopefully, together," Merkel said.
Worried by immigration and loss of sovereignty, Britons voted last year to end their country's four-decade membership in the 28-country bloc – the first nation ever to do so.
May officially triggered the two-year Brexit process in March when she was riding high in opinion polls, and called for fresh elections shortly afterwards to shore up her mandate for a tough Brexit stance.
But instead she lost her parliamentary majority, putting that hard-line approach and her political future in doubt after the disastrous June 8 election.