MPs have returned to the House of Commons for the start of two weeks of political activity that could define Britain for decades to come.
After what is expected to be days of debate, Theresa May will attempt to get her Withdrawal Agreement past MPs in the meaningful vote.
But an array of powerful – and less powerful – figures are lined up both for and against her.
These people will be the key players over the next few momentous days as the Prime Minister battles to keep her Brexit agenda, and her premiership, on track.
- Theresa May
The PM backed-off from a crunch Commons vote on the EU Withdrawal Agreement before Christmas in the face of a "significant" defeat.
With just days to go before a second attempt at a vote, and despite a festive period during which she called a slew of European leaders, no further concessions or tweaks to the deal have so far materialised.
Without something new to throw to rebellious MPs, it looks like her Brexit deal is completely dead.
- Jeremy Corbyn
The Labour leader has huffed and puffed and threatened to blow Theresa May's Brexit house down, including an attempted contempt motion against her before Christmas, but has yet to strike in anger.
He is under pressure from elements of his own party and other opposition groups who, as well as opposing the Brexit deal, want him to move a wider confidence vote against the Government, which could force a general election.
But Mr Corbyn also faces division within his party over a second referendum, so far resisting calls from members – as many as 72% according to a recent poll – who want him to back a new vote, and insisting that Labour would go ahead with Brexit if it came to power.
- Arlene Foster
The DUP leader has been flexing her party’s political muscles over Brexit as Mrs May relies on its "confidence and supply" arrangement for a slender Commons majority.
Despite Nigel Dodds, her deputy and Westminster leader, enjoying a post-New Year lunch at Downing Street last week, Mrs Foster and her party continue to insist that the backstop measures are unacceptable and the DUP cannot support them.
However, the DUP has said it will back Mrs May if she faces a confidence vote in the Commons, but only if the EU Withdrawal Agreement is voted down or significantly changed.
- Jacob Rees-Mogg
The arch-Brexiteers of the European Research Group, led by Mr Rees-Mogg, were left smarting by their failure to remove Mrs May with a Tory leadership confidence motion in December.
But a hard core of Conservative opponents to the Withdrawal Agreement are likely to follow his lead and vote it down.
Just how many MPs stay with him and how many buckle with March 29’s Brexit deadline approaching will be a key test of his influence.
- Jean-Claude Juncker
The European Commission president has been the most hostile of all senior EU figures and has made clear that negotiations will not be re-opened.
Mr Juncker has made a point of saying the EU will stand firm with the Irish government over backstop arrangements for the Irish border which would see the UK remain subject to the bloc’s customs rules if no wider trade deal is agreed before the end of a transition period.
He publicly clashed with Mrs May at a European Council summit in Brussels in December, in images which were caught on camera.
- Donald Tusk
The European Council president has been more amicable towards Britain than Mr Juncker.
Mr Tusk has repeatedly expressed sadness at the prospect of Brexit and its impact on both sides.
But he has been just as clear, warning at the same council meeting that he had "no mandate" to open new negotiations, although he would remain at Mrs May’s "disposal".
- Leo Varadkar
Ireland's Taoiseach has taken a much tougher stance on Brexit issues since taking over as Irish leader from Enda Kenny in 2017.
Heading a minority government and facing possible elections within the next few months, Mr Varadkar cannot afford to be seen to give ground to the UK at home.
Citing the need to maintain peace in Northern Ireland, Mr Varadkar has insisted that backstop measures must stay in place after the transition period "unless and until" a trade agreement is in place.
- Angela Merkel
The German Chancellor will be a major player in any moves on Brexit.
However, she is now a weakened figure after standing down as the leader of her CDU party, but remaining as Chancellor.
Mrs Merkel will be a key voice in any softening of the EU line, especially as French President Emmanuel Macron is expected to maintain a tough position.