sacred book of Zoroastrianism containing its cosmogony, law, and liturgy, the teachings of the prophet Zoroaster (Zarathushtra). The extant Avesta is all that remains of a much larger body of scripture, apparently Zoroaster's transformation of a very ancient tradition. The voluminous manuscripts of the original are said to have been destroyed when Alexander the Great conquered Persia. The present Avesta was assembled from remnants and standardized under the Sāsānian kings (3rd–7th century AD).

The Avesta is in five parts. Its religious core is a collection of songs or hymns, the Gāthās, thought to be in the main the very words of Zoroaster. They form a middle section of the chief liturgical part of the canon, the Yasna, which contains the rite of the preparation and sacrifice of haoma. The Visp-rat is a lesser liturgical scripture, containing homages to a number of Zoroastrian spiritual leaders. The Vendidad, or Vidēvdāt, is the main source for Zoroastrian law, both ritual and civil. It also gives an account of creation and the first man, Yima. The Yashts are 21 hymns, rich in myth, to various yazatas (angels) and ancient heroes. The Khūrda Avesta (or Little Avesta) is a group of minor texts, hymns, and prayers for specific occasions.

Zend-Avesta literally means “interpretation of the Avesta.” It originally referred to the commonly used Pahlavi translation but has often been used as the title of Western translations.