The concept of Nature-based Solutions (NbS) has increasingly been developed in the Conservation and Climate Policy arenas for the past 10 years at the international level. Pushed and developed by organizations such as the International Union for the Conservation of Nature (IUCN) or The Nature Conservancy (TNC), this concept has also been institutionnalizing at national/federal levels in France and the US. This research, realized in collaboration between researchers in France (INRAE, ENGEES, CNAM) and UC Berkeley, attempts to analyze the genealogy of the concept at the international level, its role within global climate and environmental policy, and how it has been unfolding at national and local levels in France and the US regarding flood policy. This talk proposes preliminary results and reflections from this on-going multi-sites research program.