Avesta texts composed orally over centuries from 1500-400 BCE in eastern Iran. Old Avestan crystallized early around 1000 BCE with no geography. Young Avestan added later with eastern Iranian place names. Transmission fixed orally before Sasanian writing in 5th-6th CE. Sasanian edition in 21 nasks divided into Gathic, manthric, legal groups. Islamic conquest destroyed most – liturgical use preserved remnants. Surviving texts tied to Yasna, Visperad, Vendidad ceremonies. Vendidad sole intact Sasanian nask on laws against demons. Khordeh Avesta for laity with prayers like Nyayeshs, Yashts. Manuscripts from 1323 CE – over 300 catalogued, mostly post-17th century. Geldner edition standard but needs update from new Iranian finds. Oral changes from recitation, Iranian language influences, phonetic shifts. No single archetype – parallel ritual and exegetical traditions. Zand Middle Persian translations oldest in Vendidad, Herbedestan.