The project proposes to experiment with the construction of a shared support methodology between SSE networks for rural entities affected by future major socioeconomic changes, through the creation of local cooperation platforms. It is mainly aimed at territories facing a necessary transformation of their economy, either because they are highly specialized in a sector (agriculture, viticulture, tourism, etc.), are threatened by climate change, or are losing attractiveness and population. Although the economic fabric of the covered territories is different, the RETSCOOP project is committed to a diversification of their economy and the development of new activities relying more on the social and solidarity economy, which is a local economy whose main objective is to respond to the needs of the population. To initiate this change, multi-actor cooperation seems to be a key success factor and will be the common thread of the proposed methodology: to put forward a shared diagnosis of the territory, a prospective vision, and an action plan with all economic, associative, institutional, and citizen actors; and to promote new activities through cooperation dynamics among these actors. Indeed, the project partners have found that there is no formalized methodology to support local entities in this global approach of changing the economic model in their territory, so the skills and experience of organizations dedicated to promoting the social and solidarity economy in France, Spain, and Portugal will be leveraged, in order to jointly develop a toolbox for rural territories.