Abstract: Grothendieck Toposes and $C^*$-algebras are two distinct generalizations of the concept of topological space and there is a lot of examples of objects to which one can attach both a topos and a $C^*$-algebra in order to study there properties: dynamical systems, foliations, Graphs, Automaton, topological groupoids etc. It is hence a natural question to try to understand the relation between these two sort different object. In this talk I will explain how to attach $C^*$-algebras and Von Neuman al gebras to (reasonable) toposes, in a way that recover the $C^*$-algebra attached to all the above examples.