"The Traite des Trois Imposteurs", ou l'Esprit de M. Spinosa is a most notorious clandestine work that was circulating throughout Europe in the 18th Century. The work is a pastiche of passages from Hobbes, Naude, La Mothe Le Vayer, Spinoza and others, contending that Moses, Jesus and Mohammed were imposters who set up their religions for political reasons. In 1990 a research seminar on the origins, nature, meaning and dispersion of the text was held under the direction of Richard H. Popkin, with the assistance of Silvia Berti and Francoise Charles-Daubert, sponsored by the Foundation for Research in Intellectual History. Advanced students and young professors carried out research projects. Lectures were given by the staff plus visiting scholars including Miguel Benitez and Bertram Schwarzbach. This volume contains the results of the seminar, including papers by the teachers and students. It breaks much new ground about the Traite, including new data about its possible origins and development, the dispersion of manuscripts of it, and its role in anti-religious Enlightenment thought.