Christianity in Iran dates back to the early years of the religion during the time of Jesus, predating Islam. The Christian faith has always comprised a minority in Iran under its previous state religions; initially Zoroastrianism in historical Persia, followed by Sunni Islam in the Middle Ages after the Arab conquest, and Shia Islam since the Safavid conversion of the 15th century; although it had a much larger representation in the past than it does today. Iranian Christians have played a significant part in the historical Christian mission: currently, there are at least 6000 churches and 380,000–1,500,000 Christians in Iran.
A number of Christian denominations are represented in Iran. Many members of the larger and older churches belong to minority ethnic groups, with the Armenians and Assyrians having their own distinctive culture and language. The members of the newer and smaller churches are drawn both from the traditionally Christian ethnic minorities and converts from a non-Christian background.
The main Christian churches in Iran are:
Armenian Apostolic Church (between 110,000, 250,000, and 300,000 adherents)
Assyrian Church of the East (about 11,000–20,000 adherents),
Catholic Church (about 21,380 adherents) in three different rites.
Chaldean Catholic Church (3,900 adherents as of 2014)
Armenian Catholic Church and Roman Catholic Church
Other particularities and churches include:
Presbyterianism, including the Assyrian Evangelical Church
Pentecostalism, including the Assyrian Pentecostal Church
Jamaʿat-e Rabbani (Iranian Assemblies of God)
Anglican Diocese of Iran
According to Operation World, there are between 7,000 and 15,000 members and adherents of the various Protestant, Evangelical, and other minority Christian denominations in Iran, though these numbers are particularly difficult to verify under the current political circumstances.
The International Religious Freedom Report 2004 by the U.S. State Department quotes a somewhat higher total number of 300,000 Christians in Iran, and states that the majority of these Christians are ethnic Armenians followed by ethnic Assyrians.