Book excerpt: The Cambridge Descartes Lexicon is the definitive reference source on René Descartes, 'the father of modern philosophy' and arguably among the most important philosophers of all time. Examining the full range of Descartes' achievements and legacy, it includes 256 in-depth entries that explain key concepts relating to his thought. Cumulatively they uncover interpretative disputes, trace his influences, and explain how his work was received by critics and developed by followers. There are entries on topics such as certainty, cogito ergo sum, doubt, dualism, free will, God, geometry, happiness, human being, knowledge, Meditations on First Philosophy, mind, passion, physics, and virtue, which are written by the largest and most distinguished team of Cartesian scholars ever assembled for a collaborative research project - 92 contributors from ten countries.