Action du groupe des tresses sur une catégorie

We describe how to define by generators and relations an action of the braid group on a category. More generally, how to define a functor from a generalized positive braids monoid, corresponding to a finite Coxeter group, to a monoidal category. Applications to constructions of Bondal (exceptional systems) and of Broué–Michel (correspondences on flag manifolds) are given. 0. Introduction...159 1. Actions...164 2. Contractibilité...171 Bibliographie...175