Ancient religion that originated in Iran based on the teachings of Zoroaster.

Founded in the 6th century BC, it influenced the monotheistic religions Judaism, Christianity, and Islam. It rejects polytheism, accepting only one supreme god, Ahura Mazda. In early Zoroastrianism, the struggle between good and evil was seen as an eternal rivalry between Ahura Mazda's twin sons, Spenta Mainyu (good) and Angra Mainyu (evil). Later Zoroastrian cosmology made the rivalry between Ahura Mazda himself (by then called Ormazd) and Ahriman. This later cosmology identifies four periods of history; the last began with the birth of Zoroaster.

Zoroastrian practice includes an initiation ceremony and various rituals of purification intended to ward off evil spirits. Fire worship, a carryover from an earlier religion, survives in the sacred fire that must be kept burning continually and must be fed at least five times a day. The chief ceremony involves a sacrifice of haoma, a sacred liquor, accompanied by recitation of large parts of the Avesta, the primary scripture.

Zoroastrianism enjoyed status as an official religion at various times before the advent of Islam, but Zoroastrians were persecuted in the 8th-10th century, and some left Iran to settle in India. By the 19th century these Indian Zoroastrians, or Parsis, were noted for their wealth and education. The small group of Zoroastrians remaining in Iran are known as the Gabars.