A Doab (Hindi: दो आब, Urdu: دو آب, from Persian: دو آب dōāb, from dō, "two" + āb, "water" or "river") is a term used in India and Pakistan for a "tongue" or tract of land lying between two confluent rivers. (See also ap-.)

The Doab, unqualified by the names of any rivers, designates the flat alluvial tract between the Ganges and Yamuna rivers in western and southwestern Uttar Pradesh and Uttarakhand state in India, extending from the Shiwalik range to the two rivers' confluence at Allahabad. The region has an area of about 23,360 square miles (60,500 square km); it is approximately 500 miles (805 km) in length and 60 miles (97 km) in width.

Doab figures prominently in history and myths of Vedic period; the epic Mahabharata, for example, is set in the Doab, around the city of Hastinapur.

The British divided the Doab into three administrative districts or zones, viz., Upper Doab (Meerut), Middle Doab (Agra) and Lower Doab (Allahabad). These districts are now divided into several other districts as enumerated below.