Voting has begun in Iran's first presidential election since its nuclear deal with world powers, as incumbent Hassan Rouhani faced a staunch challenge from a hard-line opponent over his outreach to the wider world.
The election is largely viewed as a referendum on the 68-year-old cleric's more moderate policies, which paved the way for the nuclear accord despite opposition from hard-liners.
Economic issues also will be on the minds of Iran's over 56 million eligible voters as they head to more than 63,000 polling places across the country.
The average Iranian has yet to see the benefits of the deal, which saw Iran limit its contested nuclear program in exchange for the lifting of some sanctions.
Supreme leader Ayatollah Ali Khamenei, the most powerful man in Iran, symbolically cast the election's first vote and called on Iranians to turn out in huge numbers for the poll.
"Elections are very important and the fate of the country is in the hands of all people," he said.
In the election, Mr Rouhani has history on his side. No incumbent president has failed to win re-election since 1981, when Mr Khamenei became president himself.
That does not mean it will be easy, however. Mr Rouhani faces three challengers, the strongest among them hard-line cleric Ebrahim Raisi, 56.
Mr Raisi, a law professor and former prosecutor who heads an influential religious charitable foundation with vast business holdings, is seen by many as close to Mr Khamenei. Mr Raisi has even been discussed as a possible successor to him, though Mr Khamenei has stopped short of endorsing anyone.
Mr Raisi won the support of two major clerical bodies and promised to boost welfare payments to the poor.
Mostafa Hashemitaba, a pro-reform figure who previously ran for president in 2001, and Mostafa Mirsalim, a former culture minister, also remain in the race.
The race has heated emotions and pushed public discourse in Iran into areas typically untouched in the tightly controlled state media. That includes Mr Rouhani openly criticising hard-liners and Iran's powerful Revolutionary Guard, a paramilitary force now involved in the war in Syria and the fight against Islamic State militants in neighbouring Iraq.
Mr Rouhani also found himself surrounded by angry coal miners who beat and threw rocks at his armoured car during a visit to a northern mine struck by an explosion earlier this month that killed at least 42 people.
But authorities worry about tempers rising too high, especially after the 2009 disputed re-election of former hard-line president Mahmoud Ahmadinejad that saw unrest, mass arrests and killings. Authorities barred Mr Ahmadinejad from running in Friday's election, and Mr Khamenei days ago warned anyone fomenting unrest "will definitely be slapped in the face".
Voting is scheduled to run until 6pm local time, though Iran routinely extends voting for several hours in elections. Iranian authorities say they believe the vote will exceed a 70% turnout.