The book, through a reflection on the paradigm of the informal city and with a verification in corpore vili on 10 cities, presents a description of the role that collective space and social organization have in the construction of slums. In addition, an investigation is developed on the role of architecture in the regeneration of settlements. The picture provided by the 10 factsheets on cities, in which the slums represent a phenomenon of great importance, helps to understand the reasons for their birth and development, and, through different perspectives, to understand how to promote a new comprehensive and inclusive urban organization.