This book presents a comprehensive and critical overview of historical phonology as it stands today. Scholars from around the world consider and advance research in every aspect of the field. In doing so they demonstrate the continuing vitality of one of the oldest sub-disciplines of linguistics. The book is divided into six parts. The first considers key current research questions, the early history of the field, and the structuralist context for work on sound change. The second examines evidence and methods, including phonological reconstruction, typology, and computational and quantitative approaches. Part III looks at types of phonological change, including stress, tone, and morphophonological change. Part IV explores a series of controversial aspects within the field, including the effects of first language acquisition, the mechanisms of lexical diffusion, and the role of individuals in innovation. Part V considers the main theoretical perspectives including those of evolutionary phonology and generative historical phonology. The final part examines sociolinguistic and exogenous factors in phonological change, including the study of change in real time, the role of second language acquisition, and loanword adaptation. The authors, who represent leading proponents of every theoretical perspective, consider phonological change over a wide range of the world's language families. The handbook is, in sum, a valuable resource for phonologists and historical linguists and a stimulating guide for their students.