Generally, those who are current MPs get rubber-stamped to run again, while a call goes out to members to get their names on the ballot papers in which the parties wish to challenge the incumbent. However, the calling of this general election has been used by many sitting MPs to make the decision not to run again - leaving vacant seats for which the parties now need to find new candidates. At the last count 73 MPs do not want to be re-elected to the House of Commons, taking more than 1000 years of parliamentary experience with them, and there could yet be more to come.
How common is it for so may MPs to leave?
Well, it's not really unusual for MPs to take the opportunity to go at a general election. For one thing it's easier for their party to cope with than a by-election mid-term, especially if you're in government.
And while 73 sounds a big deal, it's actually rather average. The 2010 general election saw the most MPs stand down with 149 going, while in 1997 it was 117. Indeed since 1979 the numbers have fluctuated from around 60 to 90, so this year really isn't at all out of the ordinary.
The departures do feel significant though. Perhaps because of the toxic atmosphere which has engulfed the Commons since the EU referendum, the heightened levels of abuse aimed at MPs, and of course the explusion of so many long-standing Tory MPs by Boris Johnson who was angered they voted against his Brexit deal, the roll call of those going certainly feels like a political sea change at Westminster.
So just who is going?
The only parties to be spared the exodus are the SNP and the Green Party, while the Conservatives have been hit hardest with 39 new candidates to find in seats the party currently holds.
Some "big hitters" will disappear from the green benches, including Ken Clarke, the longest serving MP in the House of Commons, Sir Oliver Letwin, former Chancellor and Foreign Secretary Philip Hammond, former Education Secretary Justine Greening, Rory Stewart, at one time a rival to Boris Johnson for leader of the party, former Home, and Work and Pensions, Secretary Amber Rudd, and current Culture Secretary Nicky Morgan.
Then there's former Defence Secretary Sir Michael Fallon, former deputy MP Sir David Lidington, and who could forget the impact of the news that the Prime Minister's brother Jo Johnson was quitting?
Other Tories include Guto Bebb, Charlie Elphicke, Claire Perry (Devizes), Sir Nicholas Soames, Alistair Burt, Richard Harrington, Richard Benyon, Sir Patrick McLoughlin, Dame Caroline Spelman, Jeremy Lefroy, Glyn Davies, Keith Simpson, Nick Hurd, Mark Prisk, Bill Grant, Sir Hugo Swire, David Tredinnick, Mark Field, Seema Kennedy, Sarah Newton, Sir Alan Duncan, Peter Heaton-Jones, Margot James, Mark Lancaster, Ross Thomson, Sir Henry Bellingham, Nick Herbert, Ed Vaizey and Sir George Hollingbery.
On the Labour side the biggest departure is the party's deputy leader Tom Watson, whose unexpected announcement last week rocked the party. Far less unsurprisingly, former minister Keith Vaz is standing down, after he was suspended from the Commons over an inquiry into his conduct by the standards committee, and so too is suspended former Labour MP Kelvin Hopkins.
One-time leadership challenger Owen Smith is going as are Jim Fitzpatrick, Sir Kevin Barron, Ronnie Campbell, Kate Hoey, Gloria De Piero, Ann Clwyd, Louise Ellman, Stephen Pound, Stephen Twigg, Roberta Blackman-Woods, Geoffrey Robinson, Teresa Pearce, Paul Farrelly, Albert Owen, Jim Cunningham, Ian Lucas, Helen Jones and Adrian Bailey. John Mann has already left and now sits in the House of Lords.
The Liberal Democrats will lose former leader Vince Cable, Sir Norman Lamb and new recruit from the Conservatives-before-she-joined-ChangeUK, Heidi Allen. The DUP say goodbye to David Simpson.
Former Labour but now independent MP John Woodcock is quitting, as is his ex-colleague Ian Austin, while Change UK founders Joan Ryan and Ann Coffey, who were Labour MPs until this year, are also standing down.
Former Tory Nick Boles will not run as an independent, the Speaker of the House John Bercow is also leaving his Conservative seat and finally, the only person who was actually elected as an independent in 2017 Sylvia Hermon, is also standing down.
Is there a common reason for so many MPs to quit now?
Brexit is ultimately the answer at the heart of so many Remainers and Leavers taking the decision to leave and not remain - certainly within the Tory party. The fundamental differences between MPs of a more pro-EU bent, and those backing the hard Brexit policy of the Johnson government has proved too much to paper over. Meanwhile in Labour there are severe Brexit divisions too, but there have been other issues cited, namely Jeremy Corbyn's leadership and lack of action in tackling anti-Semitism within the party.
Abuse around Brexit is also a reason many MPs have cited for going - Dame Caroline Spelman mentioned "the intensity of abuse arising out of Brexit", Heidi Allen said she had suffered "utterly dehumanising abuse" as an MP in a letter to her constituents, Nicky Morgan spoke of the "clear impact" on her family and "the other sacrifices involved in and the abuse for doing the job of a modern MP", while Gloria De Piero expressed concern over the "lack of tolerance for different viewpoints" within her party.
Of course some MPs, such as Ken Clarke, Vince Cable and Ann Clwyd are actually retiring, but the majority of MPs going are still young enough to try and carve out careers outside of party politics.
Are there more women than men standing down?
The simple answer is no. There are 19 female MPs going at the election, so the vast majority are men. However many more women have cited abuse as the reason to go in comparison to their male counterparts.
Tory Nicky Morgan said she has received a number of threats, including phone calls from 64-year-old Robert Vidler telling her her "days were numbered". He was jailed for 18 weeks. She said the abuse had "changed enormously" in the past decade "because of how strongly people feel about the current political situation".
Heidi Allen has also received death threats related to her stance on Brexit sent from a fake email address by 51-year-old Jarod Kirkman. He was later jailed for 42 weeks. She said: "Nobody in any job should have to put up with threats, aggressive emails, being shouted at in the street, sworn at on social media, nor have to install panic alarms at home. Of course public scrutiny is to be expected, but lines are all too often regularly crossed and the effect is utterly dehumanising."
The average age of male MPs leaving is also higher at 63, compared to 59 for females - with quitting Tory female MPs average age standing at 51.
And the average length of service for a Conservative male MP was almost 18 years, compared to 9 and a half for female MPs.