On Tuesday evening MPs will exercise their meaningful vote to support or reject Theresa May's EU-endorsed Brexit deal.
A majority are expected to snub the prime minister's withdrawal agreement in a bid to force Mrs May to come back with a new deal three days later.
But where do MPs actually go to vote before the Ayes and Nos are declared in the House of Commons?
How do MPs cast their votes?
In order for MPs to cast their votes, they walk down one of two division lobbies, one in backing the PM on her Brexit deal and the other opposing it.
This is how MPs cast their votes and there are tellers in place who count the number of people walking through the different lobbies.
How long will the Brexit meaningful vote take?
MPs will be voting for at least a couple of hours as they will have quite a few decisions to make - as they cast their votes on more than six amendments to May's Brexit deal - before the crucial vote on the agreement.
What happens if MPs back Theresa May's Brexit deal?
If - against all odds - a majority back the PM then it’s all go.
The deal should be written into law before the March 29 exit deadline, which is when the 21-month transition period begins.
What happens if MPs reject the prime minister's Brexit deal?
If MPs reject the prime minister's Brexit deal, Theresa May will have just three days to come back to the Commons Chamber with another plan.
More on the crunch Brexit vote: