Of a total population of about 65 million, more than 46 million people – all those over 15 - are eligible to vote. Some eight million of them were born after the 1979 revolution.
Voter turnout hit a record high at 80% in the 1997 elections which delivered a landslide victory for reformist President Mohammad Khatami. Women and young people were key to the vote.
But with disillusionment growing, only about 60% of the electorate voted in the final round of the 2005 election which brought hardliner Mahmoud Ahmedinejad to power.
His humble background, promises to share Iran's wealth more equally and tough words on corruption proved popular with voters.
This suggests that the desire for political reform expressed by voters in previous elections has been eclipsed by concerns about poverty and job opportunities.