The objectives of this deliverable is to understand what hinders the development and sustainability of Nature-based (Blue-Green) Solutions in the city and what could help to deploy them on a large scale. For this purpose, various professionals working on Nature- Based Solutions in the city in France were interviewed between 2020 and 2021, in the academic, institutional and operational sectors (or even at the interface between them): researchers in ecology or hydrology, IUCN (International Union for Conservation of Nature) project manager, project managers at the Regional Biodiversity Agency, director and natural environment manager of a watershed union, agro-economists engineer among others. They were asked what are the barriers and potential opportunities for Nature-Based Solutions implementation and sustainability in city. By analyzing their answers, it emerges that the obstacles are more often cultural, political or financial than technical. The potential levers often mentioned are education and awareness- raising at all levels, especially for elected officials and the general public. Regulations such as the PLU (Local Urban Plan) and new funding for more natural spaces in the city also seem to be means of promoting Nature-based Solutions in urban areas. These interviews with diverse professionals directly involved in Nature-Based Solutions in cities allow to give real courses of action to be taken to democratize these solutions throughout the French territory, or even internationally. In addition, a list of quantitative indicators is proposed to assess NBS performances and promote their implementation.