Called either Ay Yιldιz (meaning "moon star") or Alsancak ("red banner"), the flag of the Republic of Turkey depicts a white crescent moon and star on a red background. Although the crescent moon is a common symbol for Islam, it predates Muhammad by thousands of years.

The star and crescent have been found on artifacts from ancient Central Asia and Siberia and are believed to have been used in worship of the gods of the sun, moon, and stars. The symbol also has a place in ancient Greek symbology. The city of Byzantium, at the mouth of the Black Sea, was dedicated to the Greek goddess Artemis, whose symbol was the crescent moon. The flag of Byzantium thus became a white crescent moon against a field of red.