The long liturgy is the most important ceremony in Zoroastrian priestly tradition. Most extant Avestan texts have been composed for their performance within this liturgy. It is highly likely that it acquired its current form, in which it is still celebrated, during the Achaemenid period or even earlier. Like any living ceremony with a long history, it has several synchronic and diachronic variations. Nevertheless, current editions of the Avestan text recited in the liturgy do not take into account its ritual nature, synchronic variations or its evolution over time, or even the changes in the way the text itself is recited. The aim of this book is to report on the recent discoveries that raise doubts over the methodology used in current editions, and propose certain alternatives in order to further the debate.