This handbook provides a detailed and comprehensive overview of the current state of research in Celtic Language Studies, covering both existing and emerging scholarship and debate in the field, as well as containing new, cutting-edge research and highlighting fruitful directions and areas for future study. A number of special topic chapters provide additional framing, discuss special characteristics of the Celtic languages, set the modern Celtic languages in their social and cultural context, and describe currently emerging varieties of the modern languages. This book will be a useful resource not only to practising scholars who are specialists in the Celtic languages - ancient, medieval, and modern -, but also to scholars in general linguistics and linguistic typology who are interested in finding out what the Celtic languages of various historical periods are like, and students of other languages or language systems.