Nature-based Solutions (NbS) is a concept used at global and national scales in many different contexts. Used in different policy sectors, such as flood risk management, this concept is being actively promoted at the global level by environmental conservation institutions such as the International Union for Conservation of Nature (IUCN). Through this concept, nature is presented as a solution to the problems of climate change and of the erosion of biodiversity, considered as being intertwined. This concept is reframing policy discourses on biodiversity conservation, climate change adaptation/mitigation strategies, along with the sustainable use of natural resources such as water. In this presentation, we look closely at the trajectory of the concept at different policy levels, and we study in particular how this concept is being institutionalized in France and in the US. In the US, the concept has been actively promoted by the NGO The Nature Conservancy and is now adopted by many different federal agencies (NOOA, USACE, EPA or FEMA) through a voluntary promotion of the concept organized by the White House. Although the government acknowledges other co-benefits such as water quality, reducing heat, or sustaining biodiversity, this new concept seems to have a strong focus on mitigation strategies, especially regarding to flood risk, and as an alternative solution to aging gray infrastructure. If the concept is widespread, there is no common definition at a federal level and agencies have different meanings of NbS. In France, NbS implementation is focusing on biodiversity conservation and climate adaptation policy sectors, and is referring to IUCN definition as a common ground. However, there is little appropriation of the concept from the flood policy sector. NbS are being implemented through incentive mechanisms (information, coordination, financial reporting, benchmarking…) at national or regional levels, rather than command-and-control mechanisms. More generally, we will discuss what challenges this concept might bring to the fore regarding water-related risks governance.