Iraq is overwhelmingly Muslim, split between a Shia majority of around 55 to 60 percent, concentrated in the south and in Baghdad, and a Sunni minority near 35 to 40 percent, concentrated among Arabs in the west and Kurds in the north, alongside small Christian, Yazidi and Mandaean communities that have shrunk dramatically since 2003, per estimates reflected in Pew Research's Religious Composition of the World, 2010-2020.
Iraq holds sites central to Shia Islam, including Najaf, burial place of Ali, the fourth caliph and first Shia Imam, and Karbala, site of Imam Husayn's 680 CE martyrdom, commemorated annually in Ashura processions that draw millions of pilgrims and stand among Shia Islam's most important devotional practices. Mesopotamia's much older religious history, predating Islam by millennia, produced Sumerian, Akkadian, Babylonian and Assyrian religious traditions whose myths and legal codes influenced later Abrahamic religious literature, and Babylon's exile-era Jewish community produced the Babylonian Talmud, a foundational rabbinic text, before Iraq's ancient Jewish population, once numbering well over a hundred thousand, emigrated almost entirely to Israel following the 1941 Farhud pogrom and the 1950s mass exodus.