The Preliminary Discourse to the Encyclopedia of Diderot (Discours Préliminaire des Éditeurs) is the primer to Denis Diderot's Encyclopédie ou Dictionnaire raisonné des sciences, des arts et des métiers, par une Société de Gens de lettres, a collaborative collection of all the known branches of the arts and sciences of the 18th century French Enlightenment. The Preliminary Discourse was written by Jean Le Rond d'Alembert to describe the structure of the articles included in the Encyclopédie and their philosophy, as well as to give the reader a strong background in the history behind the works of the learned men who contributed to what became the most profound circulation of the knowledge of the time.