Beylerbey was a high rank in the western Islamic world in the late Middle Ages and early modern period, from the Anatolian Seljuks and the Ilkhanids to Safavid Empire and the Ottoman Empire. Initially designating a commander-in-chief, it eventually came to be held by senior provincial governors. In Ottoman usage, where the rank survived the longest, it designated the governors-general of some of the largest and most important provinces, although in later centuries it became devalued into a mere honorific title. The title is originally Turkic and its equivalents in Arabic were amir al-umara, and in Persian, mir-i miran.

The office of amir al-umara, variously rendered in English as emir of emirs, prince of princes, chief emir, and commander of commanders, was a senior military position in the 10th-century Abbasid Caliphate, whose holders in the decade after 936 came to supersede the civilian bureaucracy under the vizier and become effective regents, relegating the Abbasid caliphs to a purely ceremonial role. The office then formed the basis for the Buyid control over the Abbasid caliphs and over Iraq until the mid-11th century.