The concept of Nature-based Solutions (NbS) has increasingly developed in the conservation and climate policy arenas for the past 10 years at the international level. Promoted 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 in flood policies. This research, realized in collaboration between researchers in France 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. This talk proposes preliminary results and reflections from this on-going multi-sites research program.