The regeneration of brownfields in European metropolitan areas represents an important potential to mitigate urban sprawl by increasing density within the existing built fabric and to revitalize portions of cities at the neighbourhood scale. Although research and projects on urban brownfields are active, several issues still need to be overcome, especially regarding the sustainability transition challenge. Based on this observation, we introduce the present book, which proposes an integrated and theoretically grounded approach to highlight how urban brownfield regeneration projects—and the neighbourhood scale that they entail—can effectively contribute to the urban sustainability transitions of metropolitan areas. It is structured in two parts that are both distinct and complementary: the first part aims to clarify the framework of the investigations with definition and analysis and the second part presents a deep analysis of processes, project dynamics, and sustainability assessment approaches of urban brownfield regeneration.