Accounting for nearly 40% of global energy-related CO2 emissions and sometimes as much as 70% in large cities, buildings and construction are central to the low-carbon transition. Decarbonising buildings, especially the old stock, through energy efficiency improvements and renewable energy use, not only reduces carbon emissions, but also generates co-benefits in health, energy affordability and the labour market. Additionally, global mega-trends and the transition to a green recovery from COVID-19 provide impetus for stakeholders to take action. Cities and regions have a key role to play and can leverage prerogatives in regulation, public procurement and stakeholder engagement, while addressing multiple governance, capacity and funding gaps. To accelerate and scale up their action, cities and regions need to work with national governments to create an effective governance mechanism. Drawing on the findings of a dedicated survey of cities and regions of all sizes from both OECD and non-OECD countries, this report explains their significant role, explores sub-national policy measures, identifies key obstacles, and provides policy recommendations and a checklist for both national and subnational governments to drive the decarbonisation of buildings in cities and regions.