David Barrett's Encyclopedia of World Christianity records nearly 1.2 billion Muslims in the world. Though Muslims shared allegiance to Muhammad and to the Qur'an, Islam faced division as soon as the prophet died. Three major groups emerged over the centuries, and Islam has experienced many smaller divides.
- Vest Muslim leadership in four early caliphs: Abu Bakr (632-34), Umar (634-44), Uthman (644-56), and Ali (656-61).
- Strongly emphasize law.
- Have four major legal traditions: Hanafite, Shafite, Malikite, and Hanbalite. The Wahhabi movement that dominates Saudi Arabia grew out of the Hanbalite tradition.
- Dominate Islamic dynasties throughout history.
- Number more than 1 billion.
- Believe authentic leadership passed from the prophet Muhammad directly to Ali, his son-in-law.
- Deny the authority of the first three Sunni caliphs.
- Believe that Sunni Muslims distorted both the Qur'an and the sayings of the prophet (hadith) to reflect against Ali.
- Give martyrdom a central role in theology and ritual.
- Number more than 170 million; dominant in Iran.
- Represent the mystical tradition among Muslims.
- Emerged gradually and showed influence from both Christian and Buddhist monasticism and Greek philosophy.
- Developed in reaction to the focus on law and doctrine in early Islam.
- Became more accepted in Islam after the great Muslim thinker al-Ghazali (d. 1111) chose the Sufi path.
- Divided into orders or brotherhoods. One famous order is the Maulawiya, founded by Rumi (d. 1273), still a highly popular Islamic author.
- Practice the mystical dance of whirling dervishes.
- Combines Muslim orthodoxy with superstitions of ethnic and tribal groups.
- Often uses charms and visits to shrines of saints.
- Uses special herbs or amulets to ward off evil (as is common in Africa and the Middle East).