Talks begin amidst a politically uncertain environment, a weakened Conservative leadership and questions about the nature of Brexit itself.
The 1998 Good Friday Agreement foresees the holding of referendums on both sides of the Irish border on uniting the island if there is public support.
European Union leaders in an unprecedented show of unity will meet at a summit in Brussels where they will adopt tough guidelines for two years of Brexit talks.
Diplomats are still unsure how far apart some EU governments may be on the strategy post Brexit, though key players in Berlin, Paris and Brussels appear to be aligned.
The Scottish government is pushing for Britain and the EU to give Scotland special terms in any Brexit deal to keep it closer than England to EU markets.
Consensus will be a tall order in the coming days for the EU as they grapple with the same issues: refugees crisis, a fragile economy and Brexit.
Deaths in the Mediterranean and chaos across borders in the past year have seen a renewal of interest in offering ways for people to enter the EU legally.