The flags of many modern Islamic states feature a crescent moon and the color green. While both are regarded as symbols of Islam, they gained their association in different ways.
Some of the first recorded uses of the crescent come from the 2nd millennium B.C. where it represented the Mesopotamian moon gods Nanna and Sumer. Phoenicians spread the symbol throughout the Middle East and Northern Africa during the 8th century B.C. As these nations converted to Islam, the symbol stayed with them. The Turks began adding a star to the crescent in 12th century A.D., due to the importance of stars in the 53rd surah (chapter) of the Quran. With the fall of the Ottoman Empire in the early 20th century A.D., Turkey was left as the lone Muslim world power, further popularizing the use of both the crescent and star as a symbol of Islam. As modern Islamic states and movements began forming throughout the 20th century, they turned to the Turkish flag for inspiration.
Green, or “Greenness” is mentioned many times in the Quran and describes the state of the inhabitants of paradise and is often associated with Muhammad. Many flags of modern Islamic states such as Saudi Arabia and Pakistan feature a green field.