Chapter I
What it means
For many people the crescent and star mean Islam, as the cross means Christianity. Within Islam itself it has no religious authority: the Qur’an and the practice of the Prophet do not mention such a sign, and Islamic tradition has avoided holy images.
The crescent has nonetheless gathered real meaning for Muslims through the lunar calendar. Each Islamic month begins when the thin new moon is seen, and the sighting of the crescent marks the start and end of Ramadan.
Chapter II
Where it comes from
The crescent and star were used in the ancient Near East and on coins of the Byzantine city of Constantinople long before Islam. After the Ottomans conquered the city in 1453, the crescent became associated with their empire, appearing on banners and, in later centuries, on the Ottoman flag.
As the Ottoman Empire was the leading Muslim power, the emblem came to stand for Islam in the eyes of Europeans and then of many Muslims. In the 19th and 20th centuries it was placed on the flags of several Muslim-majority states.
Chapter III
Where you see it today
The crescent and star are on the flags of Turkey, Pakistan, Algeria, Tunisia, Malaysia and other countries, and a crescent tops many mosque domes and minarets. The Red Crescent, used instead of the Red Cross in many Muslim countries, comes from the same emblem.