At the heart of Panini's great Astadhyayi lies the concept of pratyaya, being by far the largest adhikara sutra, governing the three central adhyayas of the Astadhyayi and virtually half the sutras. This in itself bears witness to the importance of the concept in language. Indeed it has been said that to understand the Word, one needs first to understand the relation between the stem which is known and pratyaya which is unknown but joins the stem to bring forth the meaning of the whole world. This book contains a comprehensive treatment of pratyaya including its etymology, pre-Paninian and post-Paninian attestations and a thorough analysis of different categories of Pratyayas in the Astadhyayi. The translation of the six Ahnikas of the Bhasya which cover the first section of the third chapter is more literal and faithful to the text. Dr. Thompson has added critical notes which are very useful to understand the text and its context. At the end there is an attempt to uplift the linguistic notion of pratyaya to a higher spiritual level.