This report investigates the potential of nature-based solutions (NbS) to help build smart, sustainable and resilient cities. It draws from more than a decade of research and experience from G20 countries and beyond. It is informed by the rich discussions held by the energy and climate working group of the G20 in March and April 2021, as well as collateral events organized on 16 and 23 April 2021 by the Italian Presidency with the support of UNEP and UNDP.