Beykoz, also known as Beicos and Beikos, is a municipality and district of Istanbul Province, Turkey. Its area is 310 km2, and its population is 247,875 (2022). It lies at the northern end of the Bosphorus on the Anatolian side. The name is believed to be a combination of the words bey and kos, which means "village" in Farsi. Beykoz includes an area from the streams of Küçüksu and Göksu to the opening of the Bosphorus into the Black Sea, and the villages in the hinterland as far as the Riva creek. The mayor is Alaattin Köseler (CHP).