The chapters in this volume arise from presentations at a unique conference on typical and atypical language development held in Madison, USA in 2002. This joint meeting of the International Association for the Study of Child Language, and the Symposium for Research in Child Language Disorders brought together – for the first time in such large numbers – researchers from these two distinct but related fields. The week-long schedule of the conference allowed for an in-depth interrogation of their theoretical positions, methodologies and findings. In the contributions to this volume we have put together a carefully selected set of papers which from various perspectives explore the linkage between developmental theory and language impairment, and at the same time illustrate the effects of distinct conditions – hearing loss, autism, Down syndrome, Williams syndrome and specific language impairment – on the communication abilities of affected individuals. An introductory chapter, and a detailed summary which picks up recurring themes in the chapters, complete the volume.