This volume presents a study of the phenomenon of dialect levelling, the process of the reduction of structural variation. The investigation focuses on an originally rural Limburg dialect of Dutch. The approach is basically quantitatively sociolinguistic, although methods and insights from historical linguistics, dialectology as well as (linear and non-linear) phonological theory also play an important role. After a discussion of the findings, the outlines are sketched of a theory of dialect levelling. The possibilities as well as some of the problems are discussed of an integration of the study of language variation and change on the one hand and formal linguistic theory on the other.