The project began as a small commercial proposal: in 1745 the Paris publisher André Le Breton commissioned Diderot to translate Ephraim Chambers' English Cyclopaedia (1728) into French. Diderot and the mathematician d'Alembert decided translation was not enough and reshaped the work into something entirely new — not the map of individual fields but of the whole of human knowledge. The first volume appeared in 1751; the last text volume in 1765; the plate volumes continued until 1772.

The work's philosophical meaning lies as much in its order as in its authorship. D'Alembert's Discours préliminaire arranges knowledge according to the three faculties inherited from Francis Bacon — memory / history, reason / philosophy, imagination / the arts — and places theology not at the apex but beneath philosophy. In entries the Church could not openly attack — 'Carpentry' or 'Iron' — Diderot threaded subtle cross-references that, if the reader followed them, led to the demolition of canonical positions. This is both a tactic against censorship and an explicit epistemology.

The contributors include Rousseau (on music), Voltaire (on literature), Montesquieu (on taste), Turgot (on economics), and Quesnay. The plates are a quiet revolution: crafts long held to be 'lower arts' — weaving, smithing, printing, chemistry — are presented in high-resolution engravings. Reason begins not at the top but at the workbench. The project was twice condemned by the papacy (1759, 1774) and lost its royal privilege in 1759; Diderot continued the print runs in secret. When it was finished the Enlightenment had a single book — and that book was the mental world the French intelligentsia took into the eve of revolution.