In 1929 Bailey began his doctoral dissertation, a translation with notes of the "Greater Bundahishn", a compendium of Zoroastrian writings in Middle Persian recorded in the Pahlavi scripts. He became the world's leading expert in the Khotanese dialect of the Saka language, the mediaeval Iranian language of the Kingdom of Khotan (modern Xinjiang). His initial motivation for the study of Khotanese was an interest in the possible connection with the "Bundahishn". He later passed his material on that work to Kaj Barr.