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.