Jean Piaget was one of the most salient and inspirational figures in psychological and educational research of the 20th century. He was also prolific, authoring or editing over 80 books and numerous journals and papers which spawned a continuation of his work over the following decades. His work now compromises a major component of many courses on children's psychological development and in a research tradition which is expanding, scholars may need access to the original texts rather than secondhand accounts. This volume is the first of nine reproducing Piaget's original works - they are also available as a boxed set.