Mainstream adaptation to the imperatives of sustainable development remains largely technological. In a period in which governance promotes citizen participation, insurgent planning experiences multiply, as do urban co-production practices uniting civil society, universities, professionals and sometimes allies within public authorities. These initiatives carry fundamental social innovations for transitions-to-sustainability, especially in deprived areas. Rather than the greening of technologies, CoPolis insists on the importance of cooperation tools in adaptations to sustainable development. As societies increasingly claim the need to debate and the power to influence governance systems, collaborative practices can overcome some of the remaining gaps between civil society, professionals and, to a certain extent, government. They are poles of social and democratic innovation that explore concrete alternatives for reduced socio-spatial inequalities and for inclusion. France and Brazil are two countries which have a long history of cooperation and collective and community involvement in urban and professional sectors, including in the areas where the most discriminated of populations live. This project explores the potential of co-production in the adaptation to sustainability imperatives: reducing social and environmental vulnerabilities, building more democratic governance, empowering vulnerable populations and the cognitive effects of knowledge co-production. Departing from the tensions between cooperative practices and the “collaborative cul-de-sac” (Laurent, 2018), we will critically assess the impacts of these approaches on civil society, the third sector and the production of a “solidary transition urbanism”. These aspects are analysed through the mens of social and spatial justice. The project tackles three main research questions: on the origins and development conditions of these collaborations; on the relationship between political and institutional contexts and the organisational configurations of collaborative practices; and on the organisation and the circulation of knowledge within each collaboration and the role played by different types of intermediary actors. To do so, CoPolis will implement mixed methods, including qualitative research and participatory action-research protocols. We will investigate nine French and Brazilian case studies with different urban issues at stake: metropolitan megaprojects in working class neighbourhoods; large-scale urban renewal projects; and collective initiatives in housing and transition urbanisms. Moreover, the project will tackle long-lasting collaborative practices in working-class neighbourhoods and their circulation. Regarding action-research, the team will implement a survey with partners among local intermediary actors and residents. We will implement protocols to co-construct objectives, identify means for action and implementation. It will be one of the ways of observing collaborative practices. Thus, CoPolis is a comparative and participatory project, anchored in partnerships with intermediary actors and civil society organisations. In doing so, CoPolis will also assess the tangible gains due to the collaborative practices implemented during the project, in relation to the political and institutional contexts which influence organised civil society’s action possibilities. That is why the project will shed light on the conditions encouraging the emergence and consolidation of collaborative practices. At the same time, results on organisational configurations and cooperative tools will be produced. These two types of results will feed an intense effort of dissemination.