Article 115 of the constitution requires candidates to demonstrate administrative abilities, resourcefulness, trustworthiness, piety and a convinced belief in the fundamental principles of the Islamic republic.
But presidential election hopefuls also need to gain the approval of a powerful clerical body known as the unelected Guardian Council, which demonstrated in 2004 and 2005 that it was quite ready to use its vetting privileges.
Thus, of the 1010 men, women and children (ranging in age from 16 to 84) who had legally registered themselves as candidates by 14 May, only eight eventually made it past the Guardian Council for Friday's election.
All Iranians over the age of 15 are entitled to vote on Friday.
In the absence of a party political system in Iran, the council has regularly vetoed legislation it deems unconstitutional or un-Islamic. But added to this, it maintains its power to screen all candidates for public office.
In the February 2004 parliamentary elections, the council disqualified more than 2000 reformists and political moderates from standing, a move that resulted in several weeks of major political tensions.
And in June 2005, the council maintained its 25-year record of banning women from standing for the country's highest office - an issue that has provoked numerous demonstrations.
The council's decision to bar all 89
female candidates led to protests
Condemning election vetting, more than 500 intellectuals and politicians, including former members of parliament, announced in May they would boycott this year's vote.
In a statement, they said the election could not be free and fair because the Guardian Council was depriving people of free choice.
Of the few candidates that have survived to Friday's election day, the frontrunner is likely to be former president Akbar Rafsanjani.
Former education minister Mustafa Moin and Parliamentary Speaker Mehdi Karroubi may also attract a significant number of votes.
The remaining candidates are Tehran mayor Mahmood Ahmadinejad, former police chief Muhammad Baqer Qalibaf, former Revolutionary Guards head Mohsen Rezaei and former TV and radio chief Ali Larijani.