The Jean Jacques Rousseau Institute played an important role for the development of psychology and education. Moreover, it constitutes an asset for the creation and development of the IAAP by Edouard Claparède. The first Congress for Psychotechnology was held in Geneva, September 27-28th, 1920, when Edouard Claparède, then professor at the Geneva University, and Pierre Bovet, psychologist and educator, head of the Rousseau Institute in Geneva. This congress became a landmark in the history of psychotechnology. Then, the creation of an International Association for Psychotechnology took place. This was strongly supported by Geneva University, the French 'Ligue d'Hygiène Mentale de Paris', an association founded by Dr. Toulouse. Many relevant figures such as Jean Piaget joined the Institut and gave new impulse to the research on children's mind. Claparède invited him to become 'chief of research', orienting the students toward the study of different topics of child psychology. Since then, Researchers and teachers from around the world have received the impact of that center both in their doctrines and in their lives. Furthermore, many steps were given to consolidate applied psychology and the IAAP as an Association which plays a key role in the development of applied psychology.