There is a reciprocal relationship between the study of language disorders and research in normal language development. Recent studies in normal acquisition have led to a model of language development that includes not only linguistic achievements, but the development of social and cognitive abilities that lay the basis for the transition from prelinguistic communication to the use of conventional forms. This model has been applied to the study of developmental disorders of language learning. Such a model allows the more puzzling disorders of language development, such as childhood aphasia and primary autism, to be placed in a framework that predicts language disruption when underlying perceptual, cognitive, or social abilities are lacking. Assessment procedures that can be drawn from the model of language disorders are presented. It is argued that the study of these disabilities is important in the building of theoretical models of intact language processing that specify more precisely the contribution of underlying skills to overall functioning. Questions for future research that serve this reciprocal purpose are discussed.