Iranians and experts have described Friday's turnout as unusual and unprecedented as the Islamic Republic's silent majority has come out to vote in a show of protest against current government.
This is Iran's tenth presidential election since the establishment of the Islamic Republic in the 1979.
Following is a look at Iran's four candidates and their platforms.
•The incumbent is up against a fellow conservative and two reformist candidates.
•Ahmadinejad's controversial foreign policy has earned him the ire of competing candidates who accused him of bringing Iran to the brink of international isolation.
•Despite his reputation of being a radical, Ahmadinejad is the first Iranian president in decades to initiate dialogue with the country's arch foe, the United States.
•Ahmadinejad has twice invited former President George W. Bush to a public debate but his invitations were ignored.
•Ahmadinejad's election promises earned him the nickname "Islamic Robin Hood," as he promised to to share Iran's oil wealth with poor Iranians
•But his "Robin Hood" antics have been criticized as the cause of the mismanagement of Iran's economy through his "charity policy" which has given rise to inflation.
•Conservative candidate and former chairman of the Revolutionary Guards who vowed to uphold the ideological path of Ahmadinejad but with less radical foreign policies.
•Raezi promised to improve the economy by working towards an economic and security union between Iran and Arab states.
•He offered the most pragmatic view to beginning a step by step process to improve relations with the United States.
•Raezi's candidacy is seen to likely cause a split in conservative votes thereby harming Ahmadinejad's chances of winning.
•Reformist candidate whose platform appeals to religious and ethnic minorities in Iran for its promise of more political participation and social rights.
•Called for better understanding with West, especially on issues of Iran's nuclear project, however stated that Supreme Leader Ayatollah Ali Khomeini makes the final decision on progress of nuclear program.
•Karroubi criticized the incumbent's anti-Israel and Holocaust triads, accusing Ahmadinejad of harming Iran's international image over irrelevant issues.
Mir Hossein Mousavi
•Mousavi is the incumbent's main challenger in the elections.
•Mousavi said he was willing to discuss or continue dialogue with west but not at the expense of Iran's interests. "No compromise regarding Iran's interests"
•Mousavi's successful management of the economic crisis in Iran in 1981 when he instated a strict rationing program and a coupon system for food during the eight year war with Iraq earned him the reputation of a crisis manager.