In the context of knowledge and information societies, new tendencies in the long/medium term evolution of urban systems, together with new data and methods, require that existing theoretical assumptions and conceptualizations would be challenged as global urban hierarchies are reconfigured. The connection between urban systems at different levels of organization becomes more and more relevant for understanding urban systems and their transformations. But the inter-urban perspective is not sufficient to encompass these dynamics. Other cognitive, social, institutional proximities in the innovation processes combine with spatial proximities. It leads to consider cities in several dimensions of proximities in a multilayer perspective. The evolution of power distributions inside and between cities reshapes the world organization of central/peripheral cities and the complexity of the global urban system. Actors as multinational firms, or high level innovation centers, participate actively to these reconfigurations that imply the concentration of wealth, of control, of innovation and of attractiveness in few cities. In the complexity of this multi-level system, how regionalization of the world is reshaping in a multipolar urban world? How the multi-level perspective highlights some resilience properties? The methodologies derived from complex systems sciences bring new forms of intelligibility on worldwide urban dynamics.