This volume brings together ten chapters on the Celtic languages using the insights of principles-and-parameters theory. Leading researchers in the field examine Welsh, Irish, Breton and Scots Gaelic in comparative perspective, making reference to recent work on English, French, Arabic, German and other languages. The editors have provided a substantial introduction which seeks to make the volume accessible to theoreticians unfamiliar with the Celtic languages and also to Celtic specialists who are less familiar with the theoretical framework underpinning the work. The Syntax of the Celtic Languages makes a substantial contribution both to linguistic theory and to our understanding of the Celtic languages.