150,000 Tory party members will now decide who wins
The choice of the next British prime minister will be made by about 150,000 members of the Conservative Party.
After being selected as the top two candidates by Tory MPs at Westminster, Theresa May and Andrea Leadsom go on to the voting slip for a postal and online ballot, which will take place over the summer.
A campaign spending limit of £135,000 (€155,000) has been set for each candidate.
They will take part in a series of hustings around the country over the coming weeks.
The ballot closes at noon on September 9 and the winner - who requires more than 50pc of valid votes cast - will be announced shortly afterwards, allowing her to answer prime minister's questions in the House of Commons on September 14 and make her first major speech as Tory leader to the Conservative autumn conference in Birmingham on October 5.
Ballot papers will be sent out by post and email in mid-August.
But it is already too late for people to get a vote by joining the party.
The deadline for taking part in the election was three months before the close of voting - June 9.
Party members were given the right to choose their leader by William Hague when he was leader in 1998, replacing a system where only MPs had a vote.
Prior to 1965, Tory leaders 'emerged' from backroom haggling among party grandees.
In both previous contests conducted under the current system, the candidate who took first place in the initial round of the MPs' ballot failed to go on to become leader.
In 2001, Michael Portillo topped the MPs' poll in the first two rounds of voting, only to be beaten by a single vote in the final round by Iain Duncan Smith.
Michael Howard was elected unopposed in 2003 to replace him.
In 2005, there was again a contested vote, with David Davis taking pole position when MPs first cast their ballots. But David Cameron overhauled him in the second round of voting.