Nature-based Solutions (NbS) can help cities address urgent and fundamental environmental challenges by bringing ecosystems services back into cities and rebalancing cities’ relationships with their surrounding areas. By accelerating the implementation of NbS, decision-makers can help cities adapt to effects of climate change, reduce urban heat island effects and cooling needs in buildings, clean air, manage water. This report, produced by UNEP in close collaboration with the Italian Presidency of the G20, investigates the potential of NbS to help build smart, sustainable and resilient cities, drawing from more than a decade of research and experience from G20 countries and beyond. It offers an overview of the best practices of NbS implementation in cities around the world, and a set of guiding principles to improve territorial governance and establish multi-level governance frameworks to increase the impact and coherence of policies and private investments.