After months of negotiations, David Cameron will today present his draft deal on changes to the UK's membership of the EU to the other heads of state.
If the PM wants to call a June referendum, he effectively has until Friday afternoon to get all 27 heads to sign up to package of reforms.
As the summit in Brussels kicks off this afternoon, there are still parts of the deal which need to be ironed out, suggesting the meeting is more than a mere rubber stamping exercise.
However, some of the Prime Minister's critics believe this is all a carefully choreographed piece of theatre, designed to make it look as if Mr Cameron has fought hard to win concessions which amount to little more than "thin gruel".
With the deal almost done, it’s time for those politicians who have been keeping their cards close to their chest to finally reveal their hands.
All eyes are on London Mayor Boris Johnson, who on Wednesday was granted a meeting with Mr Cameron in 10 Downing Street to discuss the deal.
But it’s not just Boris who is yet to reveal if they will back Brexit.
Justice Secretary Michael Gove, Employment Minister Priti Patel and even Home Secretary Theresa May could all come out for Leave in the referendum.
Another week, and another leave group has been formed - GO Movement.
This group has sprung from Grassroots Out, with many of the same people are involved in both – including Tory MP Peter Bone, Ukip leader Nigel Farage and Ukip donor Arron Banks.
The plan is that GO Movement acts as an umbrella organisation under which other groups will sit.
It is applying for designation to be the official Leave campaign in the referendum– as is Vote Leave, the mainly Tory backed group which has repeatedly refused to merge with any organisation in which Nigel Farage is heavily involved.
Grassroots Out are holding a rally in Westminster on Friday, a stones throw from Downing Street where Mr Cameron is expected to hold a Cabinet meeting where he will suspend collective ministerial responsibility on the issue.
Perhaps a few Eurosceptic ministers will make the short walk down to the Queen Elizabeth II Centre to address the rally,
While we in the UK are fretting about whether we should stay or leave, it’s easy to forget that other countries in the EU also have a view.
A poll of Europeans conducted by Lord Ashcroft reveals the other member states' attitude towards Brexit, and while all the countries want the UK to stay in the EU, not all would had an 'at any cost' view.