Piaget's influence on psychology has been profound. His pathbreaking investigations and theories of cognitive development have set child psychology moving in entirely new directions. His bold speculations have provided the inspiration for the work of others. His studies have been the subject of many books and countless articles. And, significantly, his influence has spread to other disciplines and is having an ever-growing impact on the general culture at large.Here Jean Piaget, with the assistance of his long-time collaborator Bärbel Inhelder, offers a definitive presentation of the developmental psychology he has elaborated over the last forty years. This comprehensive synthesis traces each stage of the child's cognitive development, over the entire period of childhood, from infancy to adolescence.