Longitudinal research in human development requires more careful planning than do cross-sectional studies, and is demanding theoretically and organizationally. This volume focuses on methods of data treatment, emphasizing the importance of careful matching of methodology to the substantive problem under consideration. It deals particularly with concepts of stability and change which are central to personality and developmental research. The ultimate goal for developmental research is to understand and explain the developmental process underlying an individual's way of thinking, feeling, acting and reacting at any stage of the life process. Contributors to this volume explore the methodology and scope of life-span longitudinal studies in a variety of contexts, including intellectual and cognitive development, transitions such as that from childhood to early adult life, social mobility, behavioural genetics, and psychological disorder, particularly depression. Stressing the advantages of the prospective approach, and providing detailed analysis of the methodologies available, this volume is based on a workshop sponsored by the European Science Foundation. It will be of particular interest to social and behavioural scientists, and to research workers in such disciplines as psychology, psychiatry and epidemiology where longitudinal studies have an important place in the study of human development.