Retaining its emphasis on an uncompromising monotheism and a strict adherence to certain essential religious practices, the religion taught by Muhammad to a small group of followers spread rapidly through the Middle East to Africa, Europe, the Indian subcontinent, the Malay Peninsula, and China. By the early 21st century there were more than 1.5 billion Muslims worldwide. Although many sectarian movements have arisen within Islam, all Muslims are bound by a common faith and a sense of belonging to a single community.
This article deals with the fundamental beliefs and practices of Islam and with the connection of religion and society in the Islamic world. The history of the various peoples who embraced Islam is covered in the article Islamic world.