This paper questions the conditions of the ecological transition in the Mediterranean cities. It examines the emergence of the concept of “city in transition”. Then it observes its institutional implementation in Barcelona (Spain), Marseille (France) and Sfax (Tunisia) and focuses on their ongoing urban major projects ( 22@barcelona, Euroméditerranée, Taparura). Lastly, it analyses the ways by which the stakes of sustainable development urban have been appropriated by professionals and in the midst of local civil society.