In the time when Europe needs to strengthen its territorial cohesion and its global competitiveness, this chapter questions the integration and unity of the European urban system inherited from the long-term history as well as from the shortest-term division and reunification occurring during the second half of the twentieth century. First, we recall problems linked with the conceptual definition and delineation of cities and specify the inherited socio-spatial framework. We then detail the significant evolution of the European urban system during the second half of the twentieth century and in the beginning of this millennium due to two main processes of social and economic transition. Analyzing the concentration of activities in specialized cities enables to find metropolization processes following two different qualitative modes dividing Europe between Eastern and Western countries. Then, we discuss the question of polycentrism at different scales in connection with European policies.