It is the word that has dominated parliament, politics and public life across the UK for most of the year.
And Brexit also dominates the political leaders' New Year messages.
Labour Party leader Jeremy Corbyn says he could do it better, Liberal Democrats leader Sir Vince Cable says he wants to vote on it again, and Scottish National Party leader Nicola Sturgeon would prefer if it did not happen at all.
Theresa May is set to release her message later on Monday.
Jeremy Corbyn said: "There's so much talent across Britain but we're being held back by a system that for far too long has only served a privileged few.
"And now the Conservatives have plunged the country into crisis over the complete mess they've made of Brexit, trying to drive through a bad deal and letting people down all across the country whether they voted Leave or Remain.
"Eight years of damaging Tory failure has left us with a divided country where millions are struggling to make ends meet, where so many can't afford a home to call their own, where older people are deprived of the dignity they deserve and far too many are working in low paid and insecure jobs.
"We cannot go on like this. Labour is ready to deliver a radical alternative to rebuild and transform our country.
"We'll stand up to the powerful few so that the wealth you create is shared fairly not hoarded by a privileged elite.
"We'll work to create a society where the talent of everyone is unleashed. That's how we'll unite our country."
2:36Nicola Sturgeon said her government would work "to protect Scotland's place at the heart of Europe" in 2019.
The Scottish National Party leader said her country's reputation for hospitality "has never been more important" and that EU nationals who made homes for themselves in Scotland would always be welcome.
Ms Sturgeon, Scotland's first minister, added: "In the year ahead, the Scottish government will continue to do everything we can to protect Scotland's place at the heart of Europe.
"However, whatever the outcome of Brexit, Scotland will always offer a warm welcome to the world.
"In fact, our reputation for being an open, warm-hearted, hospitable country has never been more important.
"I want to make that especially clear to the hundreds of thousands of nationals from other European Union countries, who have done us the honour of choosing Scotland as their home.
"I know that this is a deeply uncertain time for you. But I also want you to know that your contribution to our national life – to our economy, communities and society – is hugely valued. You will always be welcome here."
Like Sir Vince, Ms Sturgeon was also hoping for some time to look at issues that were not Brexit related, such as social security, expansion of childcare, and climate change.
22:14Sir Vince Cable said the next three months would be critical, saying that the UK enters 2019 with "90 days to change the course of this country".
A second referendum is "the only way forward", he said – adding: "Are we going to make a terrible mistake, leaving behind our influence in Europe's most successful peace project and the world's biggest marketplace?
"Or are the British people, in the final hours, going to be given a chance to reconsider in light of all the facts which have come to the surface in the last two years?
"The only way forward is to have a People's Vote, with the option to Remain."
He also said that he wanted to move on to issues which had been "kicked into the long grass" by the Brexit focus, such as social care, homelessness, housing, school funding, police funding and new technology.
"Enjoy your New Year celebrations and then let's get out there and win the fight for a People's Vote and a brighter future for Britain," he added.
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Sky News
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