Iraq has many religions that make up its country, 13 to be exact. All though the religion that has more population would be Islam. There are a lot of religions that live along the mountains in Bagdad (the capital). Islam has 2 branches Sunni and Twelver Shi'i. A lot alike Iran and Bahrain Iraq has mostly Shi'i. This majority has been able too excersise political powers until the 2000's, with President Saddam Hussein and his Sunni team.
http://looklex.com/e.o/iraq.religions.htm
Islam 23,000
Shi'i 14,000
Sunni 9,000
Christianity 1,300
Nestorians 750
Chaldean Catholics 420
Syrian Catholics100
Armenian Orthodox 20
Other Christians 10
Yazidis 500
Mandeans 30
Shabak 70
Baha'i 3