[4][5] After Avestan became extinct, its religious texts were first transmitted orally until being collected and put into writing during the Sasanian period (c. 400 – 500 CE).

[10] As such, Old Avestan is quite close in both grammar and lexicon to Vedic Sanskrit, the oldest preserved Indo-Aryan language.

[13][14] Despite this, the Avestan texts never use Arya, or any other term, specifically in reference to the language itself and its native name therefore remains unknown.

[9] On the other hand, Old Avestan is substantially more archaic than either of these and largely agrees morphologically with Vedic Sanskrit, i.e., the oldest known Indo-Aryan language.

However, as for instance Sims-Williams and Schmitt have pointed out, the east–west distinction is of limited meaning for Avestan, as the linguistic developments that later distinguish Eastern from Western Iranian had not yet occurred.

[23][24] Due to some shared developments with Median, Scholars like Skjaervo and Windfuhr have classified Avestan as a Central Iranian language.

[26] Zarathustra was traditionally based in the 6th century BC meaning that Old Avestan would have been spoken during the early Achaemenid period.

As regards Old Avestan, the Gathas show strong linguistic and cultural similarities with the Rigveda, which in turn is assumed to represent the second half of the second millennium BC.

Even the Young Avestan texts are still quite archaic and show no signs of evolving into a hypothetical Middle Iranian stage of development.

[50] Due to this geographical uncertainty, as well as the lack of any dateable historical events within the texts themselves, linking any given archeological culture with the speakers of Avestan has remained difficult.

[52] Both Old and Young Avestan texts are assumed to have been composed by their respective native speakers and were possibly updated and revised for an extended period of time.

[53] Scholars like Kellens, Skjærvø and Hoffman have identified a number of distinct stages of this transmission and how they changed the Avestan during its use as the sacred language of Zoroastrianism.

[59] The transmission of this literature largely took place in Western Iran as evidenced by alterations introduced by native Persian speakers.

[60] In addition, different scholars have tried to identify other dialects that may have impacted the pronunciation of certain Avestan features during the transmission, possibly before they reached Persia.

[21] Some Young Avestan texts, like the Vendidad, show ungrammatical features and may have been partly recomposed by non-Avestan speakers.

[61] The purely oral transmission came to an end during the 5th or 6th century CE, when the Avestan corpus was committed to written form.

A large portion of the literature was lost after the 10th century BCE[63] and the surviving texts show signs of incorrect pronunciations and copying errors.

Avestan also incorporates several letters from other writing systems, most notably the vowels, which are mostly derived from Greek minuscules.

The Avestan script is alphabetic, and the large number of letters suggests that its design was due to the need to render the orally recited texts with high phonetic precision.

This is a relatively recent development first seen in the c. 12th century texts of Neryosang Dhaval and other Parsi Sanskritist theologians of that era, which are roughly contemporary with the oldest surviving manuscripts in Avestan script.

There are various conventions for transliteration of the Avestan alphabet, the one adopted for this article being: Vowels: Consonants: The glides y and w are often transcribed as and .