Urbanists have been concerned about the informal settlements proliferating in all developing countries. The concern definitely has a social and political aspect, but it also leads to a disciplinary interest in a spontaneous phenomenon that has rules of its own and puts the presuppositions of conventional urban planning into question. The barrios, villas, and favelas of Latin America are some of the manifestations of spontaneous urbanism studied in this detailed compendium of 25 interventions on informal settlements, projects aimed at improving living conditions and connected to themes like preservation, waste management, risks, infrastructures, and more.