Prime Minister Theresa May shocked the country this morning when she announced plans for an early general election on 8 June.
May will seek the approval of MPs with a motion in the House of Commons tomorrow as she seeks to bring forward the next election from its expected date of 2020.
The schedule of these elections is managed by legislation called the Fixed Term Parliaments Act, introduced under the Conservative-Lib Dem coalition government.
This set the date for all future elections as the first Thursday in May at five yearly intervals.
So what happens now?
The FTPA includes two options for early elections, but both require the approval of the House of Commons - hence May's decision to put forward a motion tomorrow.
First is the unpalatable choice, the Prime Minister could call for a vote of no confidence in her own government.
Even if May wanted to do so - and she doesn't - because the UK's election system tends to generate majority governments, this would require a Tory MPs to reject her, alongside a strong alliance of Labour, SNP, and Lib Dem MPs. It is not going to happen.
So Theresa May's plan is to use the second provision, which require two-thirds of MPs to support a motion for an early vote. And she will win.
How many votes does May need?
There are 650 MPs in parliament, meaning that May's early election plan needs support from precisely 434 MPs.
Theresa May has 330 in her own party, and Labour leader Jeremy Corbyn has already welcomed the motion for a June vote.
Corbyn leads 229 MPs. Even for a party that has struggled with discipline issues, it would be incredible for fewer than 100 Labour MPs support the motion.
What does that mean for parliament?
The FTPA also sets out when parliament must be dissolved - effectively shut down - ahead of an election.
It specifies quite clearly that this must happen 25 working days before a General Election.
Working backwards from the Prime Minister's plan of an 8 June ballot, that means that MPs will begin properly hitting the campaign trail from the first week of March.