The other, more commonly known Old Iranian language is the Avestan, a north-eastern dialect. By north-eastern is meant the south-western portion of the Central Asia and today’s Afghanistan, and also the northern Iranian province of Khorasan.

Avestan is the language in which the Zoroastrian holy book, the Avesta, has been composed. For many centuries it was primarily transmitted orally. It was not until the Sassanian period (c. 230 – 650 A.D.) that a writing system, the Avestan script, was invented for it. It must be noted that during the Sassanian period the writing system used by the Iranians was designed after an original Aramaic script (see Middle Persian section). In turn, the Avestan script was designed after the Aramaic variation which was used by the Sassanians. It is also noteworthy that the Avestan language is divided into two distinct periods: the earlier phase, which is referred to as Old Avestan, and the later period, which is referred to as Young Avestan.

The Avestan script (also known as din dabiri, dēn dibīrīh, etc.) has 54 characters, of which three consonants have two variations for each; that is to say, c, δ, r each have two forms, as we can see in the chart below. Therefore, when working with this language, we are dealing with at least 51 phonemes (short and long vowels and consonants).

The actual number of characters may vary from source to source. For instance, some scholars include glyphs for ii and uu, etc., while ii = i + i and uu = u + u (see the signs above).

The Avestan script is written from right to left, just like the original Aramaic and the Sassanian variation of it. It is probably the most comprehensive writing system ever invented; in that, it has signs for almost all the sounds that the speech apparatus can create—at least as far as the Avestan language is concerned. There are two variations (periods) of Avestan used in the extant materials: the older Avestan, the language of Zoroaster, in which his Gathas (hymns) were composed, and a younger Avestan, which is the language used in writing the additional religious materials, including the respective chapters of the Avesta. The span between the so called Old Avestan and the Young Avestan—sometimes referred to as the Younger Avestan—is several centuries. It was after the invention of the Avestan script that almost all the Zoroastrian religious texts were finally written down in the Avestan language. Before the invention of this script these texts were written in Middle Persian and other Middle Iranian languages. This was very important for the survival of the Avestan tradition, primarily because by this time the Avestan as a spoken language was already extinct.

Of the original Avesta of the Sassanian period only about a third has been left for us. Originally, under Khosrow I (Chosroes, 531-579 AD), the Sassanian king, the Avesta was divided into 21 books (called nasks), of which what is left for us is listed below:

• The yasnas: A miscellany of prayers and recitations used during the Yasnā ritual, among which are: (Y = yasna)
  • The Gāθās, Zoroaster’s hymns composed in a sort of poetry, and consisting of 17 verses, composed in Old Avestan
  • Hōm yašt, prayer to Haoma, the sacred beverage (Y 9-11).
  • Srōš yašt, hymn addressed to sraoša, god of obedience and order, also the judge in the hereafter (Y 57).
  • Frauuarāne, the Zoroastrian profession of faith (Y 12).
  • Yasnā Haptaŋhāiti, composed in OAv. (Y 35-41).
  • Yeŋhe hātąm, Ašəm vohū, yāθā ahū vairiiō (Ahunvar), three sacred parayers in Y 27.
  • A commentary on the sacred prayers (Y 22-16).
• The yašts: praise and prayer hymns. They include 21 yašts and ‘prayers.’ These are originally relations of the pre-Zoroastrian—and probably Indo-Iranian pagan—myths. The yašts are in praise of the Creator and the individual eminent deities, perhaps similar to saints or archangels, known as yazatas (‘he who is worthy of worship, (sort of) god’ from proto Iranian yaz- ‘to worship’). Over time the set has been expanded, but some of the older yašts are as follows:
  • Yašts 1-4: hymn to Ahura Mazdā and the Aməša Spəntās (the immortal holy spirits).
  • Yašt 5: hymn to Arəduuī Sūrā Anāhitā (‘the moist, strong, immaculate one’), the goddess of the waters. Therefore, the yašt is also called Abān yašt (with āb meaning ‘water’ + the plural suffix -ān). She also purifies the male semen and prepares the women’s womb for giving birth. Through this process, she purifies the human seed.
  • Yašt 6: to the Sun, also called Xvarxšēd yašt (with xvarxšēd, the New Persian xoršīd ‘sun’).
  • Yašt 7: to the moon, also called Māh yašt (with māh ‘moon’).
  • Yašt 8: to Tištriia, the star Sirius, who controls the weather and the rain; it is also called Tīr yašt (with tīr ‘arrow(head)’). He can assume different appearances: a tall young man, a bull with golden horns, a handsome white horse with golden ears, wearing a golden saddle and appurtenances, etc.
  • Yašt 9: to Druuāspa (literally, ‘he or she who has healthy horses’), the goddess who protects the quadrupeds, especially the horses and the cattle; she also protects the children and friendship, and has close affinity with Miθra. This yašt is also known as Gōš yašt.
  • Yašt 10: to Miθra, the deity governing over contract and pact; later on, he governs over the dawn as well. Since he appears before the sun, later on his name comes to mean sun, as in New Persian mehr (which is one of the many Persian words for sun). In addition, the word mehr comes to mean affections as well, due to the warmth of the sun. Therefore, the Yašt is also called Mehr yašt.
  • Yašt 11: to Sraoša (see 1, c. Y 57, above).
  • Yašt 12: to Rašnu, the god of justice and the judge in the beyond.
  • Yašt 13: to Frauuašis (literally, ‘protector’), the tutelary deities and warriors; they function as “guardian angles,” provided that we offer the proper homage to them. Also believed to be the spirit of our ancestors. But the notion is that each terrestrial being has a heavenly counterpart, who is his or her protector, hence the denimination frauuaši ‘protector.’ The yašt is also known as Farvardīn yašt (MP frawardīn).
  • Yašt 14: to Vərəθraγna, as god of victory is the smasher of resistance. He manifests himself in 10 different incarnations, including a gust, a bull with yellow ears and golden horns, a white horse with golden saddle, a camel with pointed teeth, a fierce boar, a strong youth at the age of fifteen (the much desired and favored age for a youth), a swift-winged bird (probably a bird of prey), a wild ram, a he goat, and, finally, a brave man, who possesses a sward with a golden blade. The word Vərəθraγna has been phonetically developed to Bahrām in New Persian and, therefore, the yašt is also called Bahrām yašt.
  • Yašt 15: It is called Rām yašt and it is dedicated to Rām; but in reality it is about the personification of the space between Heaven and Earth called vaiiu, who has two sides, a good and an evil one.
  • Yašt 16: called Dēn yašt; it is hymn to Čistā, the goddess who governs over knowledge and wisdom, especially that of the way to righteousness. She is usually mentioned along with the goddess Daena, who governs over human conscience and gives human the power to choose the way of righteousness.
  • Yašt 17: to Aši, the goddess of good fortune and generosity and the protectress of the family.
  • Yašt 18: Aštād yašt: to Aštād (also Arštād), one of the yazatas, who is another manifestation of justice.
  • Yašt 19: is called the Zāmyād yašt, is dedicated to the genius of the earth. Along with Aštād, Zāmyād puts the soul of the dead in a scale. However, regardless of its title, it is actually about the “royal glory of fortune,” the Kavian xvarənah.
  • Yašt 20: to Haoma, the sacred drink (see Yasna 1, b, 9-11).
  • Yašt 21: to the star Vanant, the star of the west, the guardian of goodness, and the conqueror of evil.
• The Vendīdād (also known as Vidēvdād, from imperative verb ‘anti-’ + dēv ‘demon’ + dād ‘law’, ‘the anti demons laws’ or ‘laws to keep demons away’); it is about purification rituals and the religious regulations and ordinances. It also contains some mythological materials, including some on the Creation. It consists of 22 chapters. vidēvdād is probably the only book which has been preserved for us in its entirety.
• The Visperad: some addenda to the yasnas, consisting of ritual texts and, particularly, invocations. That which is left is usually divided into 25, 27, or 32 sections.
• Hādōxt nask, on the fate of the soul after death.
• Aogəmadāeca: a sort of sermon on death.
• Ērbedestān is a Zoroastrian text on the proper procedure in matters relating to religious studies. It usually has a companion text known as the Nīrangestān or Nērangestān (~ Middle Persian nērang ‘spell, incantation, charm’).
• Pursešnīhā (also known as Pursešnīhā ī dēnīg): questions and answers regarding religious matters.
• The Little Avesta, the Persian Xorde Avestā, which consists of prayers and recitations for religious ceremonies, including:
  • The Niyāyišn (‘prayers’) to the sun, Miθra, the moon, Arəduuī Sūrā Anāhitā, Ātaš ī Bahrām (the fire).
  • The Sīrōzas, invocations of the deities in charge of the 30 days of the month.
  • The Āfrīnagān, varius invocations.
• Zoroasters Gathas, also known as gāhān is now a part of the yasnās.

The following is a fragment from the Yasnā 9:5. It describes the golden age under the kingship of Yima, the mythological Indo-Iranian god-king:

yimahe xšaθre auruuahe
nōit aotəm åŋha, nōit garəməm
nōit zauruua åŋha, nōit mərəθiiuš
nōit araskō daēuuōdātō.

pan cadasa fracarōiθe
pita puθrasca, raoδaēšuua katarascit
yauuata xšaiiōit huuąθβō
yimō vīuuaŋuhatō puθrō

‘during the kingship of the lofty Yima
there was neither coldness, nor heat;
neither old age, nor death,
nor demon-created ailments.

[it was as if everybody] roamed around in their fifteen years of age (the favored age in the Iranian tradition; see Yašt 14 above),
father and son, both alike,
as long as Yima, the possessor of good herds (the epithet of Yima),
son of Vivanghān ruled.’