Theresa May has formally announced her resignation as Prime Minister, firing the starting gun in the race to replace her.
A number of party heavyweights had already begun jostling for position in anticipation of a leadership contest after Mrs May announced at the end of March that she would make way for a new Conservative Prime Minister to lead the second phase of the Brexit negotiations.
Her resignation means the Tory leadership election will now begin in earnest. This is what happens next and who could replace her.
How is a candidate nominated?
Usually the departing Prime Minister stays on in a "caretaker" role after resigning to give the party long enough to pick a new leader. That's what David Cameron did in 2016 and what Mrs May will be doing, too.
A candidate must be formally proposed and seconded by fellow MPs.
Under the terms of the Conservative party constitution, the 1922 Committee presents to the party "as soon as reasonably practical" a choice of candidates for the election of leader.
How is the winner picked?
A ballot of Tory MPs is held in which the candidate with the least support drops off the list. This process is repeated until just two candidates remain. Candidates who realise they do not command enough support to get on the ballot may also take the decision to withdraw from the race.
Once two candidates have been selected by MPs, the Conservative Party's 150,000 members will get a vote to choose the winner.
Candidates will go head-to-head at hustings events around the country with their pitches to party members in the hope of winning their support.
A candidate achieving more than 50 per cent of the vote among Party members will be declared Leader of the Party.
Who will replace Theresa May?
Among the leading contenders to replace Mrs May are Michael Gove, Jeremy Hunt, Boris Johnson, and Dominic Raab.
Here are the latest odds on who could become the next Conservative Prime Minister when the prime minister steps down.
Can I hijack the vote?
The vote won't be open to the general public – this privilege is restricted to people who are already members of the Conservative party.
But if you're thinking of joining up with the sole purpose of influencing the result, think again: party rules stipulate the ballot will only be open to members who joined before the 'call for nominations' was opened to MPs.
Eligible voters are also required to have been a party member for three months by the time the election takes place.