This book describes and illustrates the nature of dialectical thinking as a cognitive psychological phenomenon, and makes the case that this form of cognitive organizaton is a possible successor to the adolescent formal operations stage. It uses the idea of dialectical thinking to organize theory and research on adult forms of reasoning about specific kinds of issues into a rich and coherent conceptual framework for the study of adult development. This framework makes feasible an approach to the study of adult development firmly rooted in the genetic epistemological tradition as an alternative to the approaches which currently dominate the field.