This book presents the state of the art in research on grammaticalization, the process by which lexical items acquire grammatical function, grammatical items get additional functions, and grammars are created. Leading scholars from around the world introduce and discuss the core theoretical and methodological bases of grammaticalization, report on work in the field, and point to promising directions for new research. They represent every relevant theoretical perspective and approach. Research on grammaticalization and its role in linguistic change encompasses work on languages from every major linguistic family. Its results offer valuable insights for all theoretical frameworks, including generative, construction, and cognitive grammar, and relates to work in fields such as phonology, sociolinguistics, and language acquisition. The handbook provides a full, critical assessment of every aspect of this research. It is divided into five parts, of which the first two are devoted to theory and method, the third and fourth to work in linguistic domains, classes, and cateogories, and the fifth to case studies of grammaticalization in a range of languages. It will be an indispensable source of information and inspiration for all those who wish to know more about this fascinating and important field.