This book examines the city and its rapid growth, as well as the sustainability issues it poses, in several ways. First, there is a critical approach to development, as expressed by the concept of sustainable development. The city, as a complex system, primarily refers to questions of sustainability performance, which we believe to be capable of resolving problems and difficulties, even when viewed from a local perspective, and therefore from the point of view of the areas in which it must act. Lastly, the issue of sustainability cannot be addressed without contemplating and concluding how acceptable it is to the populations concerned. All challenges raised by the urban character of the city are therefore linked to the more general question of how to define the concept of sustainable development and the sustainable city as a key area of concern.