Iraqis are voting amid tight security in the first parliamentary elections since the withdrawal of US troops three years ago.
Polling began at 07:00 local time (04:00 GMT) and closes at 18:00.
Prime Minister Nouri al-Maliki is hoping to win a third term in office amid a growing insurgency in the west of the country.
Iraq is experiencing its worst unrest since 2008, with 160 people killed in the past week alone.
Some 22 million Iraqis are registered to vote, with almost 50,000 polling stations open across the country.
The BBC’s Quentin Sommerville in Baghdad says the streets of the capital are almost empty because it is in lockdown.
He says that many of the voters will have to go on foot – the authorities have banned cars for the day in an effort to stop suicide attacks and car bombers.
Some voters face multiple searches before being allowed into polling stations.
Baghdad voter Essam Shukr, whose son died in a suicide bombing last month, told Associated Press: “We want a better life for our sons and grandchildren who cannot even go to playing areas or amusement parks because of the bad security situation. We want a better life for all Iraqis.”
Wave of attacks
While it is difficult to predict the outcome of the poll, Mr Maliki is still expected to be a pivotal figure in the coalition-building process which will follow the election.
His State of Law alliance, a Shia coalition, has largely avoided the fragmentation seen by other political blocs since the last election
Our correspondent says that a result should not be expected any time soon. It took nearly 10 months to assemble a government after the last election, he says, and it is likely to take quite a lot of horse trading this time.
The campaign has so far been a violent one, with 50 people killed on Monday when soldiers, police and overseas citizens cast their votes.
One bomb struck a Kurdish political rally in the town Khanaqin, killing 30 people and wounding at least 50 others.
On Friday, at least 31 people were killed as a series of blasts targeted a Shia election rally in Baghdad. The Islamic State in Iraq and the Levant – an al-Qaeda offshoot – said it had carried out the attacks.
However, the BBC’s Rafid Jaboori says he has travelled to various places in Iraq over the past few days and people have been telling him the violence will not put them off voting, particularly in the Shia heartland of the south and the autonomous Kurdistan region.
More than 9,000 candidates are competing for 328 parliamentary seats. There will be no voting in parts of Sunni-dominated Anbar province, where security forces still battle Islamist and tribal militants for control of the provincial capital Ramadi and nearby Falluja.
Source: BBC