Zend Avesta

The Avesta /əˈvɛstə/ is the primary collection of religious texts of Zoroastrianism, composed in the otherwise unrecorded Avestan language.

The Avesta texts fall into several different categories, arranged either by dialect, or by usage. The principal text in the liturgical group is the Yasna, which takes its name from the Yasna ceremony, Zoroastrianism's primary act of worship, and at which the Yasna text is recited. The most important portion of the Yasna texts are the five Gathas, consisting of seventeen hymns attributed to Zoroaster himself. These hymns, together with five other short Old Avestan texts that are also part of the Yasna, are in the Old (or 'Gathic') Avestan language. The remainder of the Yasna's texts are in Younger Avestan, which is not only from a later stage of the language, but also from a different geographic region.

Extensions to the Yasna ceremony include the texts of the Vendidad and the Visperad. The Visperad extensions consist mainly of additional invocations of the divinities (yazatas), while the Vendidad is a mixed collection of prose texts mostly dealing with purity laws. Even today, the Vendidad is the only liturgical text that is not recited entirely from memory. Some of the materials of the extended Yasna are from the Yashts, which are hymns to the individual yazatas. Unlike the Yasna, Visperad and Vendidad, the Yashts and the other lesser texts of the Avesta are no longer used liturgically in high rituals. Aside from the Yashts, these other lesser texts include the Nyayesh texts, the Gah texts, the Siroza, and various other fragments. Together, these lesser texts are conventionally called Khordeh Avesta or "Little Avesta" texts. When the first Khordeh Avesta editions were printed in the 19th century, these texts (together with some non-Avestan language prayers) became a book of common prayer for lay people.

...
Wikipedia