The Anatolian beylik of Menteş (1260–1424), with capital in Milas in southwest Anatolia and headquartered in Beçin castle near that city, was one of the frontier principalities established by OghuzTurkish clans after the decline of the Seljuk Sultanate of Rum. The Beylik was named after its founder, Menteş Bey. It had come into existence by the year 1290. The beylik's core territory corresponded roughly to ancient Caria or the later Muğla Province in Turkey, including the province's three protruding peninsulas.
Menteş Beys submitted to Ottoman power for the first time in 1390 under the reign of Bayezid I the Thunderbolt. After 1402, Tamerlane restored the beylik to Menteşoğlu İlyas Bey, who later recognized Ottoman sovereignty in 1414. It was incorporated into the Ottoman realm in a definite manner in 1426.
The present-day Muğla Province of Turkey was named the sub-province (sanjak) of Menteşe until the early years of the Republic of Turkey, although the province seat was moved from Milas to Muğla with the establishment of Ottoman rule in the 15th century.