Despite being engines of development, innovation and interaction, cities can also exacerbate some of the world's most serious environmental and socio-economic challenges. It is therefore necessary that cities are planned and designed with nature in mind. Nature-based solutions (NbS) are capable of helping cities to address urgent and fundamental environmental challenges. This report, produced by UNEP together with the Italian Presidency of the G20, studies the potential of NbS to build smarter, more sustainable and more resilient cities. It shows an overview of NbS implementation practices in cities around the world and a set of guiding principles for improving territorial governance and establishing multilevel governance frameworks to increase the impact and coherence of policies and private investment.