International audience ; The Piaget "genetic epistemology" has renewed our conceptions of human cognition and makes his theory of development a reference in child psychology and adolescent. But is often criticized for describing a hypothetical subject, "epistemic", which has nothing to do with the topic psychological situation. In fact, in this approach, education, social factors still involved second: they depend on the development, facilitate the endogenous development but are not constituents. Piaget has striven to measure knowledge, whenever possible, regardless of family or school learning. These guidelines contrast with the positions of LS.Vygotsky, Piaget contemporary psychologist born the same year as him, but died prematurely in 1934 and we are also celebrating this year in 1996, the centenary of the birth. Their theories are radically opposed to reasons related to the theoretical assumptions of the authors, and biographical data including the very different socio- historical contexts in which they lived. Vygotsky is part of the revolutionary impulse in Russia and in the heart of new educational experiences inspired by dialectical materialism. He is a man of letters and his first book in 1925 entitled "Psychology of Art". He is interested in human sciences, philosophy, linguistics, history, literature, theater. If the psychology of Piaget is driven by the idea of continuity between the biological and the psychological level, that of Vygotsky, such as H. Wallon, is brought in part of his Marxist anchor by the idea of rupture, discontinuity, conflict. Break between the biological and psycho -social levels of development, which led him to give a decisive role in the cultural tools (intellectual, technical, human and artistic productions, symbolic systems and languages ) in the construction of thought. Wallon considers that "the individual is genetically social", that biological extensions in the culture that is according to Marx "the inorganic body." The child in this design is early in strict dependence ...