Islam in Iran
The overwhelming majority of Iranians--at least 90 percent of the total population--are Muslims who adhere to Shia Islam. In contrast, the majority of Muslims throughout the world follow Sunni Islam. Of the several Shia sects, the Twelve Imam or Twelver is dominant in Iran (most Shias in Bahrain, Iraq, and Lebanon also follow this sect). All the Shia sects originated among early Muslim dissenters in the first three centuries following the death of the Prophet Muhammad in A.D. 632.
The principal belief of Twelvers, but not of other Shias, is that the spiritual and temporal leadership of the Muslim community passed from Muhammad to Ali and then sequentially to eleven of Ali's direct male descendants, a tenet rejected by Sunnis. Over the centuries various other theological differences have developed between Twelver Shias and Sunnis.
Although Shias have lived in Iran since the earliest days of Islam, and there was one Shia dynasty in part of Iran during the tenth and eleventh centuries, it is believed that most Iranians were Sunnis until the seventeenth century. The Safavid dynasty made Shia Islam the official state religion in the sixteenth century and aggressively proselytized on its behalf. It is also believed that by the mid-seventeenth century most people in what is now Iran had become Shias, an affiliation that has continued.
- "Iran: Religious Life." U.S. Library of Congress Country Studies, December 1987.