This book of new work by leading international scholars considers developments in the study of diachronic linguistics and linguistic theory, including those concerned with the very definition of language change in the biolinguistic framework, parametric change in a minimalist conception of grammar, the tension between the observed gradual nature of language change and the binary nature of parameters, and whether syntactic change can be triggered internally or requires the external stimuli produced by phonological or morphological change or through language contact.