The twin problem of helping students synthesise separate aspects of psychology and, as research workers, familiarising each other with our own thinking - prompted the series of seminars on which this volume is based. This book, like its associated seminars, represents not only the interests of the authors but also the needs of students, both undergraduate and graduate, for whom it has been prepared. The seminars were held in the Psychology Department at the London School of Economics and Political Science. This book aims to present an integration of some of the research problems that are current by showing how each is concerned with the problem of knowing and understanding and how together they throw light on some of the issues raised by Piaget.