The seventeenth-century French philosopher was not a marginal figure: he was an active agent who existed at the heart of the multiplicity of knowledge networks which have fundamentally shaped our understanding of the modern human condition. By turn mathematician, theologian, doctor, lawyer, alchemist, poet, geographer, historian, and physician, the figure of the philosopher was protean. Even those works and lives which seem the least significant can reveal - and this is the book's hypothesis - unexpected connections between currents of thought, methods, and institutions. Eight thematic introductions, 690 entries, and a historical and well-reasoned index make up this Dictionary. 167 specialists have contributed to it, creating an essential tool for the new exploration of the seventeenth-century philosophical landscape.