Diyar Mudar (Arabic: دِيَارُ مُضَرَ, romanized: Diyār Muḍar, lit. 'abode of Mudar') is the medieval Arabic name of the westernmost of the three provinces of al-Jazira (Upper Mesopotamia), the other two being Diyar Bakr and Diyar Rabi'a. According to the medieval geographer al-Baladhuri, all three provinces were named after the main Arab tribes that were settled there by Mu'awiya I in the course of the early Muslim conquests of the 7th century. The Diyar Mudar was settled by the Mudar tribe.
Diyar Mudar encompasses the region on both banks of the middle course of the river Euphrates, from the area of Samosata to the town of Anah, and includes the area of the Balikh River and the lower reaches of the river Khabur. Its main cities were Raqqa in the south and Edessa (al-Ruha in Arabic) in the north, and other major cities included Harran, and Saruj (now Suruç).