Although the core of Jean Piaget’s scientific legacy is his stage model of intellectual ontogenesis and his studies of the reasoning skills that figure in those stages, his impact on education, especially American education, has been vast. Thirty years ago, his theory of cognitive development stimulated revolutionary changes in preschool and elementary school curriculum practices, and in the ensuing decades, Piagetian thought has continued to foment major changes in American education, with the whole language approach to reading instruction being a recent illustration. The aim of the present chapter is to focus attention on those aspects of Piaget’s contributions that have proven to be of greatest significance for educational psychology. The chapter begins with a biographical sketch. The rest of the chapter deals with Piaget’s views on learning. This material is divided into 2 sections. The first section presents Piagetian ideas about the relation between cognitive development and learning, and it summarizes findings from classical experiments that tested those ideas. The second section presents Piagetian ideas about instructional methodology and also summarizes findings from classical experiments that tested those ideas.