This chapter discusses 'Islamicization' of Iranian society. Iranian society after the Arab conquest has gone through crucial socio-economic and cultural changes that led to reconstruction of the pre-Islamic society of Iran according to new Islamic rules and norms. Iranian society since the early sixteenth century witnesses the appearance of two 'national' centers of power which in coexistence and conflict have played a crucial role in the social events and development of Iran: state authority, and Religious authority. The appearance of some ideological and theological Shi'ite schools was also important for legitimizing and further increasing of the ulama's power and right to authority in the society of Iran. The reign of the Safavids and the Shi'itization of Iran led to the construction of a powerful Shi'ite religious authority and an increase in the ulama's power in bazaar.