Albeit by no means new, collaboration in science has recently gained unprecedented momentum and visibility. Commonly presented as “a good thing”, it has become an imperative. This holds especially true for sustainability science, a recent and expanding problem-driven science that focuses on the dynamic interactions between nature and society and aims to create and apply knowledge in support of decision making for sustainable development. Researchers in this field are strongly encouraged to work with colleagues from other disciplines and actors from outside academia. Yet, little is currently known about how collaborations transform the work practices and identities of researchers and contribute to the shift towards more sustainability. COLLAB² will offer both a broad and in-depth view of inter- and transdisciplinary collaborations in sustainability science. It will pursue the four following goals: 1) elaborate a typology of these collaborations, based on a thorough investigation of their characteristics; 2) describe and analyse their dynamics: how they unfold over time, what stimulates or on the contrary hinders them, at various levels; 3) explore their effects on the practices, roles, identities and trajectories of researchers and their collaborators, and their capacity to contribute to the shift towards more sustainability. A fourth cross-cutting goal is to conduct this research and disseminate its results in close association with sustainability scientists and their partners, so that this project about collaboration will itself be highly collaborative (hence the acronym COLLAB²). COLLAB² will explore the full scope of collaborations in sustainability science in three institutional settings aiming to foster them: CNRS’s Zones Ateliers and Observatoires Hommes-Milieux, and biosphere reserves. It will produce a balanced and multi-level analysis of collaborations, and address their different dimensions (material, cognitive, relational and affective) in the long run. A common research framework will be adopted to allow a cross analysis of the data. It will rely on a mixed method, combining bibliometric tools, a national questionnaire that will be disseminated simultaneously in the three institutions, and an ethnographic survey of a sample of diversified collaborative projects. COLLAB² will devote paramount attention to the perspectives of participants in collaborations, which is crucial given the importance of their human factors but has seldom been addressed so far. COLLAB² will bring together six social and life scientists with strong personal experience of collaborations in sustainability science and wanting to explore them together and with other partners. A dyad of collaborators from each institution investigated will be closely associated to the work of the consortium throughout the project. This will enable us to experiment with a process of participative and iterative reflection through the sharing of experiences and ideas beyond the consortium, leading to new knowledge and mutual learning. COLLAB² will thus make an invaluable contribution to the emerging scientific field of collaboration studies. Its results will be disseminated to a large and diversified audience, using well-adapted language and through a wide array of communication channels (articles in academic and technical journals; conferences and seminars; presentations to the institutions investigated; short videos; interactive website). It will help sustainability scientists and their collaborators to identify the factors and effects of collaborations, overcome their inherent difficulties and form a community of practice. It will provide science policymakers and relevant ministries with concrete recommendations to improve collaborations in sustainability science and craft sound research policies in the Anthropocene.