All languages change, just as other aspects of human society are constantly changing. This book is an introduction to the concepts and techniques of diachronic linguistics--the study of language change over time. It covers all the major areas of historical linguistics, presenting concepts in a clear and concise way. While examples are given from a wide range of languages, most major concepts and techniques are illustrated by material drawn from the languages of Australia and the Pacific. The needs of undergraduate students of linguistics have been kept firmly in mind, but the book will also be of interest to the general reader seeking to understand language and language change. This third edition includes a number of rewritten and supplemented sections and new material on grammaticalization, ergativity and accusativity, language diversification, palaeolinguistics, and morphological evolution.