Avesta or Zend-Avesta, the prayer book of Zoroastrianism. It forms the sacred books of the present-day Zoroastrians known as Parsis, who live in small communities in Iran and in India and Pakistan. The original home of these worshipers and of their holy scriptures was ancient Persia, and the faith they profess was that founded by the ancient Persian Zoroaster, one of the great religious teachers of the East. The doctrines of this ancient belief and a record of the customs of the earliest period of Persian history are preserved in the Avesta.

Flourishing six centuries before the Christian era, the religion represented by the Avesta may have been the faith of the Achaemenids, the dynasty of the Persian kings Cyrus the Great, Darius I, and Xerxes I. The religion lost adherents after the conquest of Persia by Alexander the Great in the 4th century bc, and many of the sacred books were lost. It was revived but was then virtually destroyed in the 7th century ad by the Muslims in their victorious invasion. Most of the Zoroastrians were then compelled to accept the Qur'an (Koran), the sacred scriptures of Islam; many, however, fled to India for refuge and took with them what was left of their sacred writings. A few of the faithful remained behind in Persia and, although persecuted, they continued to practice their religion. These two groups, about 80,000 persons in India and 18,000 in Persia, were responsible for the preservation of the Avesta in its present form.