Nature-based Solutions (NbS) are a recent policy tool used notably to limit and cope with water-related risks such as flood risks while preserving biodiversity. This concept has been produced and defined at a global scale through institutions such as the World Bank and the International Union for the Conservation of Nature (IUCN), but nowadays many countries have adopted it and are implementing projects qualified as NbS. NbS can be seen as an innovative way of overcoming the classical opposition between flood risk protection versus ecological preservation and could prompt positive changes, helping to reframe policy debates about climate change adaptation, increasing the participation of citizens into risk management policy and planning, while reconciling risk mitigation and biodiversity conservation strategies under a common framework. In particular, NbS are supposed to enable inclusive, transparent and empowering governance processes, according to IUCN NbS Global Standards produced in 2020. NbS projects are supposed to enable more stakeholders’ participation that technocratic classical gray infrastructures. However, so far, little is known about how this globally-defined concept actually unfolds at national and sub-national scales and these assumptions have to be analyzed in practice. In this talk, we compare four cities, Angers and Strasbourg (France) and San Francisco, California, and Portland, Oregon, (United-States), to highlight how Nature-based Solutions are implemented, focusing on governance analysis. More precisely, we focus on how the governance of these projects was/is being developed at the stage of project definition, project implementation, and project monitoring/evaluation. Governance is defined as the patterns of rules and practices that enable the implementation of a policy/project, focusing not only on centralized nor State authority, but on how actors from private, civil and public society interact in the policy-making. This communication is grounded within a bi-national research project (US/France) comparing how Nature-based Solutions are implemented in France and in the US in the context of flood risk management.