The attacks were the latest in a surge of unrest that has left more than 4,200 people dead this year, the highest toll since 2008 when Iraq was emerging from a brutal sectarian war.
At least seven car bombs went off across Baghdad from around 5:00 pm (1400 GMT), when Iraqis are typically shopping or visiting cafes, killing 26 people, security and medical officials said.
The deadliest of the bombings hit the eastern neighbourhood of Zafraniyah, where at least six people were killed.
No group immediately claimed responsibility for the attacks, but Sunni militants linked to Al-Qaeda often use coordinated car bombings in a bid to target Iraq's Shiite majority, whose adherents they regard as apostates.
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"The continuing car bomb wave phenomenon is increasing in volume," Jessica Lewis, an analyst at the Washington-based Institute for the Study of War, told AFP.
"Casualty levels seem to be getting bigger," she said, adding that targeting civilians helped the militant group gain publicity.
Violence in northern Iraq killed another seven people, all of them members of the security forces.
Six policemen were killed in the attack and two seriously wounded.
A separate attack west of Mosul, a primarily Sunni Arab city that remains one of Iraq's least stable, left a soldier dead.
In Fallujah, a former insurgent bastion west of the capital, militants wearing explosive belts attacked a police station and traded fire with security forces.
Three of the bombers were killed when their explosives blew up while a fourth militant was shot by police, officials said, adding that 12 policemen were wounded, including two officers.
Authorities insist a campaign targeting militants is yielding results with hundreds of suspects captured and dozens more killed.