Iranians are heading to the ballot box on Friday in a run-off presidential election that pits reformist candidate Masoud Pezeshkian against hardliner Saeed Jalili after last week's vote failed to produce a clear winner.
Some 61 million people are eligible to vote for a successor to president Ebrahim Raisi, who died in a helicopter accident in May.
Polling stations open at 8 am (0430 GMT) and close at 6 pm, although authorities could allow them stay open later. The first results are expected on Saturday.
Turnout in last week's vote hit a record low and none of the candidates gained an absolute majority. Pezeshkian gained around 42.5% of the vote and Jalili won 38.7%. There were two other candidates in the first-round vote.
The election comes amid a severe economic crisis, as well as tensions with the West and regional powers in the Middle East. Frustration among the public with the enforcement of state authority, especially among the younger population, is running high.
Many Iranians, especially young people, have however lost faith in the possibility of seeing major political change at home.
The death of the young Kurdish woman Mahsa Amini in autumn 2022 sparked nationwide protests against the Islamic system of rule, but the protests were quashed with harsh punishments for demonstrators.
The president is only number two in Iran's power structure as Supreme Leader Ayatollah Ali Khamenei functions as the head of state and has the final say in all strategic matters. He is also commander-in-chief of Iran's armed forces.