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 (ithna- ashari), 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.

Islamic Conquest of Iran
The beduin Arabs who toppled the Sassanid Empire were propelled not only by a desire for conquest but also by a new religion, Islam. The Prophet Muhammad, a member of the Hashimite clan of the powerful tribe of Quraysh, proclaimed his prophetic mission in Arabia in 612 and eventually won over the city of his birth, Mecca, to the new faith. Within one year of Muhammad’s death in 632, Arabia itself was secure enough to allow his secular successor, Abu Bakr, the first caliph, to begin the campaign against the Byzantine and Sassanid empires.
Shia Islam in Iran
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.
Sunni Islam in Iran
Sunni Muslims constitute approximately 8 percent of the Iranian population. A majority of Kurds, virtually all Baluchis and Turkomans, and a minority of Arabs are Sunnis, as are small communities of Persians in southern Iran and Khorasan.
Bahai
The largest non-Muslim minority in Iran is the Bahais. There were an estimated 350,000 Bahais in Iran in 1986. The Bahais are scattered in small communities throughout Iran with a heavy concentration in Tehran. Most Bahais are urban, but there are some Bahai villages, especially in Fars and Mazandaran. The majority of Bahais are Persians, but there is a significant minority of Azarbaijani Bahais, and there are even a few among the Kurds.
Christianity in Iran
Iran’s indigenous Christians include an estimated 250,000 Armenians, some 32,000 Assyrians, and a small number of Roman Catholic, Anglican, and Protestant Iranians converted by missionaries in the nineteenth and twentieth centuries. The Armenians are predominantly urban and are concentrated in Tehran and Esfahan; smaller communities exist in Tabriz, Arak, and other cities.
Judaism in Iran
The Constitution of 1979 recognized Jews as an official religious minority and accorded them the right to elect a representative to the Majlis. Like the Christians, the Jews have not been persecuted. Unlike the Christians, the Jews have been viewed with suspicion by the government, probably because of the government’s intense hostility toward Israel.
Zoroastrianism in Iran
Like the Christians and Jews, the Zoroastrians are recognized as an official religious minority under the Constitution of 1979. They are permitted to elect one representative to the Majlis and, like the other legally accepted minorities, may seek employment in the government. They generally enjoy the same civil liberties as Muslims. Although Zoroastrians probably have encountered individual instances of prejudice, they have not been persecuted because of their religious beliefs.