Conservative MPs have begun casting their votes in the first ballot in the race to succeed David Cameron at Number 10.
The Chairman and Deputy Chairman of the 1922 committee, Graham Brady and Charles Walker, will add up the results after voting closes at 6pm and declare them in the evening.
Liam Fox, Theresa May, Stephen Crabb, Andrea Leadsom and Michael Gove are standing in the contest.
The candidate with the lowest level of support will be eliminated, after which four MPs will remain.
What happens then?
The next round of voting will take place on Thursday before a final round next Tuesday to reveal the two candidates who will be put forward to Tory members in a postal ballot.
When will the successful candidate take over?
The winner will take over as Tory leader and prime minister by September 9 "at the latest", the Party has announced.
Who's the favourite?
Ahead of the first ballot, a poll by the Conservative Home website of 1,214 party members gave Mrs Leadsom a narrow lead with 38 per cent, one point ahead of Home secretary Theresa May - widely seen as the frontrunner - on 37 per cent.
In contrast a YouGov poll for The Times of 994 Conservative Party members suggested that if it came to a final round run-off between the two women candidates, Mrs May would win by by 63 per cent to 31 per cent.