Iran's official religion is Twelver Shia Islam, and about 90 to 95 per cent of Iranians are counted as Shia Muslims, making Iran the largest Shia-majority country in the world. Sunni Muslims, mainly Kurds, Baloch and Turkmen, make up most of the rest, about 5 to 10 per cent. The constitution also recognises three ancient minorities, Zoroastrians, Jews and Christians, each with reserved seats in parliament. The Baha'i faith, which began in Iran and is its largest non-Muslim minority, is not recognised and faces systematic persecution. Since the 1979 revolution Iran has been an Islamic republic, in which a senior cleric, the Supreme Leader, holds the highest office in the state.
Official figures describe a nation that is almost entirely Muslim. The history beneath those figures is layered: Iran was the birthplace of one of the world's oldest religions, the home of one of its oldest Jewish communities, and a Sunni land for most of its Islamic history before it became the centre of Shia Islam.
Yazd and the Fire of Zoroaster
Before Islam, the religion of Iran was Zoroastrianism, founded by the prophet Zarathustra, known to the Greeks as Zoroaster, at a date scholars still debate, somewhere between about 1500 and 500 BCE. It taught of a supreme god, Ahura Mazda, and a cosmic struggle between truth and falsehood, ideas that some historians believe later influenced Judaism, Christianity and Islam. The Achaemenid kings, beginning with Darius I, invoked Ahura Mazda in their inscriptions at Behistun and Persepolis. It was the religion of Persia's great empires and the official faith of the Sasanian empire from the third century CE until the Arab conquest.
The desert city of Yazd is still the centre of Iran's small Zoroastrian community, about 25,000 people. Its main fire temple keeps a flame that tradition says has burned since about 470 CE. On the hills outside town stand the Towers of Silence, circular stone enclosures where the dead were once laid out to be exposed to vultures, so as not to pollute earth or fire. They were used until the mid-twentieth century. Zoroastrianism also lives on among Iranians of every faith, in the spring New Year festival of Nowruz, the fire-jumping night of Chaharshanbe Suri and Yalda, the longest night of the year, all pre-Islamic celebrations that the Islamic Republic has never managed to replace.
Hamadan and Susa: An Ancient Jewish Community
Jews have lived in Iran for about 2,700 years, since the exiles of the Assyrian and Babylonian conquests. In 539 BCE Cyrus the Great took Babylon and allowed the Jewish exiles to return to Jerusalem and rebuild the Temple, which earned him an honoured place in the Hebrew Bible. Many stayed. In Hamadan, a domed building is venerated as the tomb of Esther and Mordecai, heroes of the Book of Esther, and near ancient Susa lies a shrine held to be the tomb of the prophet Daniel, visited by Muslims as well as Jews.
The community numbered around 100,000 before 1979, and most emigrated after the revolution, largely to the United States and Israel. Fewer than 10,000 remain, mainly in Tehran, Isfahan and Shiraz. They are represented by one reserved seat in parliament and still have working synagogues, kosher butchers and schools.
From Arab Conquest to Persian Revival
Arab armies conquered the Sasanian empire between 633 and 651, and Islam spread slowly over the following centuries. Iran became Muslim without becoming Arab. Persian survived as the language of culture and government, and around 1010 the poet Ferdowsi completed the Shahnameh, the epic of Iran's pre-Islamic kings, written in Persian with very few Arabic words. Persian-speaking poets such as Rumi, Saadi and Hafez made the Persian tradition of Sufi mysticism central to Islamic literature. Hafez's tomb in Shiraz is still a place where Iranians go to recite his verses and open his book at random for guidance.
For most of this period, though, Iran was mainly Sunni. The Shia communities were a minority, concentrated in cities such as Qom.
Isfahan and the Safavid Turn to Shia Islam
That changed in 1501, when Shah Ismail I founded the Safavid dynasty and declared Twelver Shia Islam the state religion. The choice set Iran apart from its Sunni rivals, the Ottoman Empire to the west and the Uzbeks to the east. The Safavids brought Shia scholars from Jabal Amil, in what is now Lebanon, to build a clerical establishment, and converting the population took about two centuries.
Their capital, Isfahan, still shows the result. Its great square, Naqsh-e Jahan, is lined by the Shah Mosque and the Sheikh Lotfollah Mosque, masterpieces of Safavid tilework. Across the river lies New Julfa, the Armenian quarter founded when Shah Abbas moved thousands of Armenian merchants and craftsmen there in the early seventeenth century. Its Vank Cathedral combines a Persian dome with Christian frescoes. Iran's Christians, mostly Armenians and Assyrians, are a recognised minority with three reserved seats in parliament. Their ancient monasteries in the north-west, including St Thaddeus, are a World Heritage Site. Muslims who convert to Christianity, however, face prosecution.
Mashhad and Qom: The Shia Heartland
Twelver Shia Islam holds that leadership of the Muslim community belonged to twelve imams descended from the Prophet's cousin and son-in-law Ali. Only one of the twelve is buried in Iran: the eighth, Imam Reza, who died in 818. His shrine in Mashhad has grown into one of the largest religious complexes in the world, visited by tens of millions of pilgrims a year. The city of Qom, around the shrine of his sister Fatima Masumeh, is the country's great centre of religious learning. Its seminaries train clerics from across the Shia world, and Ayatollah Ruhollah Khomeini taught there before his exile in 1964.
The defining moment of the Shia year is the month of Muharram, which commemorates the killing of the Prophet's grandson Husayn at Karbala in 680. On Ashura, the tenth day, processions of mourners fill the streets, and in many towns communities stage ta'zieh, traditional passion plays of Husayn's martyrdom, which UNESCO recognises as intangible heritage.
Tehran: Religion as the State
The revolution of 1979 overthrew Shah Mohammad Reza Pahlavi and created a state built on Khomeini's doctrine of velayat-e faqih, rule by an Islamic jurist. The Supreme Leader, a senior cleric chosen by the elected Assembly of Experts, commands the armed forces and sets the direction of policy. Khomeini held the post until his death in 1989, and Ali Khamenei succeeded him. The Guardian Council, six clerics and six jurists, vets every law against Islamic principles and can bar candidates from elections. Islamic law also governs family law, and since the early 1980s women have been legally required to cover their hair in public.
That requirement became the focus of the largest protests in decades after the death of 22-year-old Mahsa Amini in the custody of the morality police in September 2022. Women removed their headscarves in public, and the slogan "Woman, Life, Freedom" spread across the country and abroad.
Sunni Iran on the Frontiers
Iran's Sunni Muslims live mostly on its edges, among ethnic minorities whose communities extend across the borders: Kurds in the west, near Iraq and Turkey; Baloch in the south-east, near Pakistan and Afghanistan; Turkmen in the north-east; and some Arabs along the Gulf coast. The constitution guarantees respect for the Sunni schools of law, and Sunni-majority areas run their own seminaries and mosques. In practice, Sunnis complain of discrimination in senior government posts, and for decades they have been unable to build a Sunni mosque in Tehran, so worshippers there pray in private halls.
The tensions are sharpest in Sistan and Baluchestan, the poorest province, which is also mainly Sunni. On 30 September 2022, during the national protests, security forces opened fire on crowds after Friday prayers in the provincial capital, Zahedan, killing dozens of people in what residents call "Bloody Friday". The city's leading Sunni cleric, Molavi Abdolhamid, became one of the most prominent critics of the government from inside the country.
The Baha'is and the Gap Between Figures and Belief
The Baha'i faith began in Iran in the nineteenth century with the Báb, executed in Tabriz in 1850, and Bahá'u'lláh, whose teachings about the unity of religions now have followers worldwide. In Iran, where there are an estimated 300,000 Baha'is, the faith is regarded as heresy and not recognised. Since 1979 more than 200 Baha'is have been executed or killed, and Baha'is are barred from university and much public employment.
How religious Iranians are today is also debated. Official statistics count almost everyone as Muslim, but an independent online survey in 2020, by the Netherlands-based group GAMAAN, found far lower levels of religious identity, with many respondents describing themselves as non-religious or spiritual. The survey has limits, since it reached people online, but it suggests large differences between official Islam and private belief. The wider Shia world, including the holy cities that Iranians visit, is covered in our overview of religion in Iraq, and the language that carried Iran's culture through the conquests is explained in our guide to the Persian language.