In the last years, the traditional dichotomy in International Law between jus ad bellum and jus in bello has been more and more abandoned in favour of a system comprising norms designed to create fair and sustainable peace. It has been recognized that post-war societies need help in order to avoid a relapse into conflict and chaos. But what is the essence of this just post bellum? What are its sources? Did the introduction of a Responsibility to Protect (R2P) change the rather sceptical attitude by most governments towards peace-building activities that were often considered as intrusive?In this contribution it will be shown that the contours of the jus post bellum are still rather unclear but on the other hand it is very likely that this concept is here to stay.