This book showcases the latest research from the world's leading experts on Celtic linguistics. The 15 chapters span a variety of linguistic subdisciplines as well as theoretical and methodological perspectives. Together, these articles highlight critical aspects of contemporary inquiry into the linguistic systems of Breton, Cornish, Irish, Manx, Scottish Gaelic, Welsh and their ancestor languages. The volume is organized around four key sub-areas: (1) Syntax and Semantics, (2) Phonology and Phonetics, (3) Language Change, Historical Linguistics and Grammaticalization, and (4) Sociolinguistics and Language Documentation. The volume's papers offer detailed investigations of current theoretical issues in Celtic syntax, semantics, phonology, and phonetics, as well as of language policy and ideology, language weaponization, and diachronic and synchronic language change. These state-of-the-art contributions represent the impressive diversity of the field of Celtic linguistics and emphasize the wide body of work being conducted in the language communities of the six Celtic nations.