This book is designed as a textbook for students and is written with full coverage of each of the topics along with enough examples and with as much clarity as possible. In Chapter 1, the issues involved in the matter of subgrouping are discussed in detail and evidence, some old and some new is presented for the classification. Chapter 2 is a revised version of my 1983 book. All recent developments are incorporated in it. It has also been shown in a few places that some rethinking and modification are necessary on topics that appeared so far to be well established and beyond questioning. A welcome deviation from earlier works in the planning of the chapter on comparative phonology is that the changes in each individual language are collected together in one place. This will be of immense help to a reader who wants to know the changes that have affected a particular language. When a change goes back to a proto stage of two or more languages, it is discussed fully under one of the languages (the first language according to the order adopted) and a reference to it is given under the other language(s)). In each case, cognates are given only from one or two sister languages the selection of which depends on the absence of the change under discussion; one should consult Burrow and Emeneau 1984 for the full list. In a group of cognates, the meaning given for the first or the previous word holds good for the subsequent words not accompanied by any meaning. From §2.3, where the bare rules are given taking each proto sound as the starting point, one can find out not only the languages in which the particular sound has undergone a change but also the nature of the change involved in each language. Grateful acknowledgements are due to the Annamalai University, Annamalainagar, where I taught this and other related subjects for thirty-seven years and developed my ideas through that experience. I owe gratitude to that University also for publishing most of my earlier books. I must express my gratitude to the University Grants Commission and P. S. Telugu University, Hyderabad, for awarding me Emeritus Fellowship for the years 2001-2003 during which period I started work on this book. I wholeheartedly thank my colleagues, friends and old students who readily supplied me with photo copies of books and articles that are not otherwise accessible to me. But for their unstinted cooperation, I could not have written this book. I am grateful to Professor D. N. Shankara Bhat, Professor S. V. Shanmugam and to Professor K. Murugaiyan for going through parts of the manuscript and offering useful suggestions. I express my gratefulness to Professor Udaya Narayana Singh, Director, Central Institute of Indian Languages, Mysore, for including this book in the publication programme under the Centre of Excellence for Studies in Classical Tamil - Scheme for Classical Tamil. My special thanks are also due to Professor K. Ramasamy, Professor-cum-Deputy Director (Head, Scheme for Classical Tamil), Central Institute of Indian Languages, Mysore, for taking keen interest in the book and for taking all necessary steps for its publication. Last but not least, I wish to thank my wife, Satyavati, for all encouragement in my academic pursuits ensuring at the same time that I take adequate care of my health. P. S. SUBRAHMANYAM