The chapter is based on fieldwork conducted in Tehran and it examines the idea of Zoroastrians as an ethnic group constructed by the social leaders of the community in Tehran. The collective identity, primarily based on common beliefs and religious practices, is strengthened by ethnic elements, such as customs, historical genealogy, specific personality traits, belonging to a particular territory, and dialects of the Zoroastrian Dari language. The language has been neglected during the 20th century to some extent, but now some of the Zoroastrians take interest in it, perceiving Dari as the value and symbol of Zoroastrian purity. From this perspective, Zoroastrians are perceived as an ethno-historical community with an essential experience of persecutions from Muslims over the centuries, as well as a biological-racial community. The years of isolation under Muslim rule, as well as the prohibition of apostasy from Islam and of the promotion of non-Islamic religions as incorporated within the legal system of the Islamic Republic of Iran, support the idea of being born as a Zoroastrian (zartoszti-zāde). Using Danièle Hervieu-Léger’s term, Zoroastrianism was turned into an ethnic religion to survive in the face of a weakening identity.