The Radical Enlightenment refers to a fascinating movement within the Enlightenment that challenged traditional forms of religious, philosophical, and political authority and promoted social reform, freedom, democratic values, social equality, and libertas philosophandi. The study of the Radical Enlightenment focuses on the thought of freethinkers, atheists, pantheists, Spinozists, political reformers, and other kindred spirits. Over the last thirty years scholarly writing on, and about the very notion of, a Radical Enlightenment has proliferated and research on the matter has moved in different directions. This research companion provides a timely and comprehensive overview of current research on this matter, gathering together leading experts who cross the boundaries of geographical terrain, of discipline, of intellectual position and of methodology. In addition to dealing with canonical authors and celebrated texts, such as Spinoza and his Tractatus Theologico-Politicus, authors discuss many less well-known figures and debates from the period whose importance is only now being appreciated.