The four related lectures contained in this volume were held at the College de France (Paris) in May 2001 and are compiled under the title Ritual, Word and Thought in the Old and New Avesta: (1) the question of the Zoroastrianism ritual tradition and the so-called anti-ritualistic focus within the gathish-avestish literature, with a critical discussion of the recent polemics concerning the chronology and the character of the historical person Zarathustra; (2) the theme of the interiorization of rituals in consideration of the function of ritual practices with respect to the holy scriptures and the efficacy of the myyra-; (3) the nature and function of aua- between ritual and ethics, with a general description of the Indo-Iranian setting, with particular consideration of the relationship between nta-, druh- and annta-; a further chapter concerns the definition of the role of Zarathustra in the Gythys as well as his supposed "mythic" and "literary " dimensions. (4) The final lecture discusses the determination of the "religious orientation" of the Ancient Avestan literature in comparison with the later mazdyyasnistic texts in Avestish, Old Persian and Pahlavi. The volume includes complete indices. It is of value for scholars with an interest in Indo-Iranian philology and linguistics, as well as for historians of religion.