Come October, David Cameron will no longer be Conservative leader or prime minister.
But who could replace him? We look at the potential contenders.
- Boris Johnson
While he previously claimed that he had as much chance of becoming Prime Minister as being "reincarnated as an olive", Boris Johnson is now the bookies' favourite to replace David Cameron.
The former London mayor summoned friendly Conservative MPs to his Oxfordshire home at the weekend in what is thought to have been a likely preparation for a run.
As one of the leaders of the Brexit campaign, Alexander Boris de Pfeffel Johnson, his standing among Eurosceptic Conservatives is currently high.
However, ex-minister Alan Duncan said that despite Mr Johnson's "excitement and notoriety", many activists did not want a "permanent ride on the big dipper".
Sources close to Boris say that if he is elected as leader and Prime Minister, he would not hold a snap general election.
- Theresa May
Although a remain supporter, Theresa May was not a vocal one and has come out of the furore relatively unscathed.
Ms May has been Home Secretary for six years, a post that often destroys politician's careers, showing her durability.
The Conservative MP is second favourite and she is reported to have been courting the party's rank and file in preparation for Mr Cameron's departure.
Some MPs, such as Iain Duncan Smith, have said that the next leader of the Tories should be a leave supporter.
International Development Secretary Justine Greening has appealed to Mrs May and Mr Johnson to form a "united leadership" to help bring the country back together.
- Stephen Crabb
Hugely popular in the Conservative parliamentary party, Stephen Crabb comes from a working-class background.
In a possible hint that he may run, the work and pensions secretary said: "The party should be led by someone who understands the enormity of the situation we're in and who has got a clear plan to deliver on the expectations of the 17 million people who voted to come out last week."
But some believe the contest may have come too soon for the relatively inexperienced minister.
- Nicky Morgan
The Education Secretary has not ruled out running to be the next leader of the Tories, saying that one of the final two candidates who party members choose between should be a woman.
"If that is me or someone else it is too early to tell," she said.
"I would think about it but it is about what other colleagues are looking for in the next leader."
The Loughborough MP would represent a moderate continuation of Cameron's legacy, however, her support for remain may count against her.
- Sajid Javid
The business secretary has long been talked about as a future leader of the Conservative party.
However, in recent months Sajid Javid's chances have taken a hit.
Former colleagues have claimed that he backed remain while privately supporting Brexit.
The former managing director at Deutsche Bank's handling of the Tata Steel crisis also drew criticism.
Mr Javid says the "party has lots of talents" on both sides of the argument and he is "not going to guess" who will be in the running.
- Ruth Davidson
The Scottish Conservative leader has impressed many with her performance during the EU referendum campaign, and with her success in the elections north of the border last month.
However, a Westminster seat would be needed for Ruth Davidson to have any viable shot at becoming the next Prime Minister and she has suggested the job is not really for her, describing life at No 10 as "lonely".
- Liam Fox
The former defence secretary was one of the first to confirm he was considering a fresh bid to become leader of the Conservative party, having unsuccessfully sought the job in 2005.
An outspoken supporter of Brexit, he would be popular among Eurosceptic Tories.
- Andrea Leadsom
The energy minister has not ruled out running for the top job, saying that she was "looking at all sorts of angles and considering".
A vocal Brexit campaign saw the former banker and fund manager gain prominence within the Tory party and sparked talk that she is seeking rapid promotion to the top job.
- Priti Patel
Another vocal Brexit campaigner, Priti Patel saw her public profile increase in the run-up to the EU referendum.
The employment minister is on the right of the Conservative Party and supports capital punishment for the most serious crimes.
- Jeremy Hunt
Although the health secretary backed the remain campaign, Jeremy Hunt revealed on Good Morning Britain that he is "seriously" considering putting himself forward to be the next leader of the Conservative Party.
Mr Hunt has said that Britain should have a second referendum on the terms of exiting the EU if it can secure a new deal to control its borders.
- How is a candidate nominated?
A potential candidate must be formally proposed and seconded by fellow MPs, and agree to abide by the rules.
On Tuesday the Conservative Party board will meet to approve the timetable proposed by the executive of the 1922 Committee which represents Tory backbenchers.
Formal nominations will begin on Wednesday when the 1922 Committee gathers for its weekly meeting and rubber stamps the process.
Nominations will close at midday on Thursday, assuming the process meets approval.
On Monday, if there are more than two challengers, Conservative MPs begin to vote to whittle them down in consecutive rounds. In each round the candidate with the least votes is eliminated.
Hustings are scheduled around the country for when the candidates go head-to-head with their pitches to party members.
A winner is expected to be announced between mid-August and September 2 depending on the length of the Parliamentary stage and how long it takes to set up the hustings and ballot.
- What happened last time?
In 2005, the last time a new Conservative leader was needed, Kenneth Clarke went out in the first round, followed by Liam Fox, leaving David Cameron to battle it out with David Davis.
There were 11 hustings around the country with rivals going head-to-head.
David Cameron received 134,446 votes to David Davis' 64,398.
In total 78% of the 253,689 eligible Conservative party voters took part.