TEHRAN ― More than 50.5 million people are eligible to vote for a new presiden to succeed Ahmadinejad, who is barred from standing for a third consecutive term under the constitution.
Polling stations open at 8:00 am (0330 GMT) on Friday and close 10 hours later, although if there is a massive turnout the interior ministry can extend voting until midnight.
At the same time as choosing a new president from six candidates, voters will also pick municipal councillors.
Iran's supreme leader Ayatollah Ali Khamenei, who has called for a large turnout but not publicly stated his preference for any single candidate, will vote early.
If no candidate secures 50.1 per cent or more of the votes to win outright on Friday, a second round will be held a week later.
The first results are expected on Saturday. ― AFP/VNS