The religion that uses a crescent moon and star symbol is Islam. The symbol is used widely on the flags of many Muslim countries, and it is also used on one of the flags for the International Federation of Red Cross and Red Crescent Societies.
The crescent moon and star symbol existed before Islam was formed. There is little information on the symbol's origins, but some evidence shows that the symbol was used in Central Asia and Siberia as part of celestial worship. The city of Byzantium, now known as Istanbul, was first to use the symbol. When the city was conquered by Muslims in the 15th century, the symbol was adopted by Islam.