Zab is the name given to two separate rivers that flow through Iran, Iraq and Turkey to become the two principal tributaries of the Tigris.

The Great Zab (Zab Ala) rises in the mountains of southeastern Turkey and flows south for 265 miles (426 km) before joining the Tigris south of the city of Mosul. It forms the approximate boundary of the Kurdish-populated region of Iraq and is used as the political boundary of the Kurdish Autonomous Region. In 750 AD, the Great Zab was the scene of the Battle of the Zab between the Umayyads and the Abbasids.

The Little Zab (Zab Asfal) rises in northwestern Iran and flows southwest for 250 miles (402 km) through Iraq to join the Tigris north of the town of Baiji.

The rivers are extensively used for irrigation and hydroelectricity, with major dams on both rivers.