A look at election rules in Iran:
Who can run: Under the Iranian Constitution, candidates for president must be Muslim and between the ages of 25 to 75. There are differing interpretations about whether women are eligible for the presidency, but the ruling clerics have blocked all potential women candidates. Parliament permits women and members of religious minorities to run. People with criminal records or high-ranking officials of the toppled monarchy are banned from running for elected office.
Reaching the ballot: All hopefuls for high elected office must be cleared by the Guardian Council, a 12-member body of clerics and scholars loyal to the ruling theocracy. The council often rejects potential candidates considered too liberal or critical of the Islamic system. For Friday's election, just four of more than 470 possible candidates were allowed.
Who wins: A simple majority _ 50 per cent plus one vote _ is needed to win the presidency. If no candidate attains that Friday, a second round is held between the two top vote-getters on June 19.
Who votes: Anyone at least 18 years old. There are more than 46.2 million eligible voters for Friday's election _ with about a third of the voters under 30. The figure includes millions of Iranians living abroad. Iran's overall population is more than 70 million.
President's role: The president has control of some domestic policies and serves as the international face of the country. But the non-elected theocracy, headed by Supreme Leader Ayatollah Ali Khamenei, controls all major decisions and directly oversees key government posts such as the foreign, intelligence and defense ministers.