This conference explores philosophical writings that circulated clandestinely in the early modern era—a corpus of some 250 texts in some 2,000 manuscript copies. At its most radical, the clandestine philosophical tract remained rigorously anonymous. These tracts offered a rationalist criticism of philosophy and religion, drawing on classical and Renaissance alternative traditions while providing critical readings of mainstream texts to bring out their errors and ideological slight of hand. Many of the ideas expressed in the manuscripts emerged in print in the works of Voltaire, Hume, d’Holbach, and Diderot. The conference examines how these manuscripts enable a reading of European intellectual history beyond the official professions of faith promoted by the schools and established authors.