Nature-based Solutions (NbS) are instruments usually presented as the nexus between climate and biodiversity policies. Indeed, these solutions were put at the agenda of the last COP26 and COP15. In the context of flood risk management, they can be seen as an innovative way to overcome the classical opposition between flood protection and river restoration projects. However, so far, little is known about how this globally defined concept unfolds at national and sub-national scales. Through interviews with stakeholders, surveys and the analysis of specific case studies, the project “Nature-Based Solutions from Theory to Practice” analyzes how this concept is being institutionalized in the USA and in France and how NbS projects are implemented and evaluated in both countries. Preliminary results show that while in France this new concept makes a clear emphasis on biodiversity issues, in the USA it seems to have a strong focus on mitigation strategies, especially regarding to flood risk reduction in the face of climate change, and as an alternative solution to aging gray infrastructure. This presentation will focus on the type of (des)integration of climate and biodiversity policies NbS enable at global level ; national levels (US and France) and local levels through case studies analysis.