The contribution of this volume to the literature on peer learning is its focus on approaches that reflect a common concern with cognitive processes based in developmental, information processing, or more generally, constructivist perspectives on peer learning. Although the clear importance of the social context of peer learning is not ignored, the volume's emphasis is on the cognitive growth that occurs within the learning environment. Any discussion of peer learning involves consideration of who is learning, how the role of peers with whom one works can be conceptualized, what it is that peers learn together, what changes as a result of the interaction, and how we can know what occurs in groups or what has been learned. The chapters in this book speak to these questions. The key question underlying many of these others is why we should worry about the intricacies of peer interaction. Both the practical and theoretical reasons for doing so are delineated. The developmental theory presented in the Introduction lays the foundation for the later descriptions of specific techniques, though many of the techniques reflect a range of other influences as well. Part I presents the implications of the work of two major theorists in cognitive development, Piaget (Ch. 1) and Vygotsky (Ch. 2). In Part II, six chapters describe a variety of peer learning techniques or models of collaboration, many of which are influenced by the work of Piaget and Vygotsky. The chapters in Part III consider the role of the teacher and the skills needed when using peer learning as an instructional strategy. The Conclusion points to areas in which further research is needed. This volume is based on original papers presented by the contributing authors in November 1996 at the Rutgers Invitational Symposium on Education on Cognitive Skills and Learning With Peers.