Almost 300,000 local and international observers will monitor the elections, and the US military plans to send heavy deployments of troops onto the streets during the voting.
More than 14,000 candidates are competing for 440 seats in 14 of the country's 18 provinces.
The vote will not include the three autonomous Kurdish provinces, Arbil, Dohuk and Sulaimaniyah, all in the north.
Elections have also been postponed in the oil-rich Kirkuk province, which the Kurds want to incorporate despite fierce opposition by the central government.
For weeks, colourful posters and banners with pictures and slogans have been put up across the country and festive campaign rallies held.
The killing of three Sunni Arabs candidates on Thursday and a Shia contender two weeks earlier raised fear of more violence.
Iraqi and US military commanders have in recent days warned that al-Qaeda poses a threat to the elections.
Hundreds of women, including teachers and civic workers, have been recruited to search female voters after a rise in female suicide bombers last year.
A roadside bomb found south of Baghdad on Friday killed three officers and wounded 17 others, an Iraqi police official said.
Campaign rules prohibit the use of government resources and gifts to voters, and restrict the use of religious symbols.
The independent electoral commission said it had received very few complaints about attempts of vote buying, but the issue has become a talking point among Iraqis.
Qassim al-Aboudi, a representative of the electoral commission, said it had fined three political lists for campaign violations, but he declined to identify them or their misdemeanours.
"We received very few reports about attempts to buy votes and we will take action against these parties," he said.
In a Baghdad park this week, a leading Shia party distributed blankets with a pamphlet inserted in the folds instructing voters which candidates to choose.
Other parties have given out watches to win favour, and in one case, equipped a teenage football team with uniforms.
Nuri al-Maliki, the prime minister, rejected media reports about attempted vote fraud.
"We want to show the world our elections are transparent," he said.
Mithal al-Alusi, a parliamentarian who heads a secular list of candidates, accused some parties of using state funds.