Urban planning is the science that, at different scales, deals with the organization of territories; the goal is to allow the community to carry out the different activities of urban and territorial life.Since the beginning of time, people had to give themselves rules of coexistence, including the rules for use of all public areas. Therefore, in other words, before we had the modern urban planning discipline, people have always practiced urban planning, both spontaneously and applying theories but also working off utopias.After recalling the foundation cities of ancient history, the production of ideal urban models and cities built in the Fascist period, this contribution focuses on the “foundation of the city in the city”, or the “invention” of the neighborhood residential and, in particular, the Italian economic and popular housing neighborhood.The foundation of the new residential areas, that is, of “small cities” realized ex-novo, triggers, inter alia, the break with the historic city and the new process of urban expansion and establishes the concept of suburbs.The case studies examined in the Italian production of Edilizia Residenziale Pubblica –ERP (i.e., Public Residential Housing) neighborhood and, more recently, of the requalification and recovery interventions that concerned them, are also addressed in terms of neighborhood, comparing them to international case studies. In particular, we explore the dimensions of sustainable development, capable of effectively activating both natural capital and functional and social mixité.