The Islamization of Iran occurred as a result of the Muslim conquest of Persia in 633–654. It was a long process by which Islam, though initially rejected, eventually spread among the population on the Iranian Plateau. Iranian peoples have maintained certain pre-Islamic traditions, including their language and culture, and adapted them with Islamic codes. These two customs and traditions merged as the "Iranian Islamic" identity.
When did Iranians convert to Islam?
Unlike the popular opinion that Arabs converted Iranians to Islam after defeating the Sasanian Empire, Iranians continued to practice their native religions for many centuries. The conversion to Islam was a slow process which was aided by differentiated tax systems for Muslims and non-muslims.