Islam is a monotheistic Abrahamic religion representing about one-fifth (20%) of the world's population. It is an religion which began in the early 600's by the prophet Muhammad.
Muslims believe that Jews and Christians have misinterpreted their own texts. Muhammad is not seen as having started a new religion, but as the restorer of the original, uncorrupted faith of Adam, Abraham, Moses, Noah, and Jesus.
It is believed that Muhammad, the final prophet, had the Koran revealed to him by Allah (God) through the angel Gabriel.
The main Muslim holy book is the Koran (also spelled Qur'an).