Zoroastrianism /ˌzɒroʊˈæstriənɪzəm/ (or Mazdaism) is a religion and philosophy based on the teachings of prophet Zoroaster (also known as Zarathustra, in Avestan) and was formerly among the world's largest religions. It was probably founded some time before the 6th century BCE in Greater Iran.

In Zoroastrianism, the Creator Ahura Mazda is all good, and no evil originates from him. Thus, in Zoroastrianism good and evil have distinct sources, with evil (druj) trying to destroy the creation of Mazda (asha), and good trying to sustain it. Mazda is not immanent in the world, and his creation is represented by the Amesha Spentas and the host of other Yazatas, through whom the works of God are evident to humanity, and through whom worship of Mazda is ultimately directed. The most important texts of the religion are those of the Avesta, of which a significant portion has been lost, and mostly only the liturgies of which have survived. The lost portions are known of only through references and brief quotations in the later works, primarily from the 9th to 11th centuries.