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.
The Preliminary Discourse to the Encyclopedia of Diderot is arguably one of the best introductions to the French Enlightenment, giving forth the idea that man possesses the capability, through his own intelligence and analysis, to alter the conditions of human life. The Encyclopedia constituted a demand of the intellectual community for a refinement of all of the branches of knowledge in reference to past and recent discoveries. Such a compilation of human knowledge would be both secular and naturalistic, discrediting theology as the primary basis. The Discourse, although created by d'Alembert, was actually a result of collaboration with other "men of letters" aiming towards the same progressive goals of the Enlightenment. Three of these major contemporary philosophes that undoubtedly contributed to the guiding philosophies and beliefs of the "Discourse" include Denis Diderot, Jean-Jacques Rousseau, and Étienne Bonnot de Condillac, with whom d'Alembert was known to have been in contact. These men shared a passion for the dissemination of scientific knowledge. And, although this time period would seem unfavorable to such an endeavor, with Europe undergoing massive political upheaval and general instability, the time was ripe for their ideals to take hold. A thriving community of professionals, aristocrats, and clergy became increasingly responsive to the exchange of ideas that came to characterize and serve as the foundation for the cooperative compilation of information in this Encyclopedia.