This work is constituted from studies each of which, in a first version, was to be given as a lecture or in a separate publication in France or abroad. We have, however, reshaped and rethought them in order to integrate them in this volume, which arranges the results of several years of reflection on Hobbes's oeuvre. This ordering and the reshuffling that it implies makes it possible to draw out issues which were only implicit in the texts’ first versions. Also, it clearly appeared that these are at the same time the fundamental problems and concepts of modern political thought, which were analysed from the different angles under which Hobbes's philosophy is considered. Some studies aiming to confront the English philosopher's positions with those of some of his contemporaries (Gracián, Filmer, Pascal, etc.) will also emphasise the displacements and ruptures which run across modern thought.