The Avesta is the oldest extant primary source of Zoroastrian literature, although the term "Avesta" designates not one text but a group of texts written in the Old Iranian language called Avestan, attested from the 2nd to 1st millennia BC.
[4] New Persian was adopted relatively late for one or more of several possible reasons, including religious and/or conservative attachment to the use of the earlier Pahlavi, a desire to maintain distance from languages primarily or newly expressed in the Islamic world, and potential distance from the main locales where New Persian was being used.
[5] The first surviving text of this nature is the Zarātoštnāma ("Book of Zarathustra"), also known as the Mawlūd-e Zartošt ("Birth of Zarathustra"), written by Kaykāvūs ibn Kaykhosrow, although later attributed to the poet Zartošt b. Bahrām Paždū, himself the author of numerous works including the Čangranaghāčanāma.
In 1700, it was translated by Thomas Hyde, making it among the earliest Zoroastrian texts known to Western scholars.
In the 19th century, the Parsis (Zoroastrian community of the Indian subcontinent) began to use Gujarati as their primary language of writing; the Parsis adopted the use of printing early on and so quickly came to begin publishing books, pamphlets, newspapers, and journals.