Many studies are shifting their attention from the sustainability of a single building to the one of the entire urban system. This is the reason why we decided to focus on the research of policies that allow to achieve a more sustainable way of life for the entire urban system. Starting from the first chapter, we discuss the European and international targets designed to keep the emissions produced under certain levels and to have a shift to a decarbonised society. Moreover, we also analyse several case studies to categorize their main features and the measures applied to improve the sustainability at the district and urban level.