This brief biography of Jean-Baptiste Say facilitates the putting into context of the thought of an author who would have been twenty-three years old in 1789. His original background is that of Geneva protestant. The political action of La Décade is manifest in his commentaries, article reviews and political statements. The originality of this action lies in the fact that he seeks to invest the field of ideas in all its dimensions: institutions, elites, places of scientific research. In choosing teaching, Say follows the tradition of the ideologues. The Revolution demonstrates the power of people and their ideas on the course of events. The ideas in Traité d’économie politique and Cours complet cannot be understood without a reconstruction of the different influences that would contribute to shaping the thought of Jean-Baptiste Say. JEL Codes : B12