n the Mélanges philosophiques for Catherine II, Diderot, resuming a project of the Empress, insisted on the need to draw up a small moral catechism based on the Petit code de la raison humaine written by his friend Jacques Barbeu Du Bourg. This work, banned by French censorship (1772), was published in London by Benjamin Franklin (1770, 1772/1773), then in The Hague, by Marc-Michel Rey, with a false imprint (1774). This article tries to reconstruct the network that promoted the dissemination of the Petit code and in which form it was presented to the Empress.