In sustainability science, revising the paradigms that separate humans from nature is considered a powerful ‘leverage point’ in pursuit of transformations. The coupled social-ecological and human-environment systems perspectives at the heart of sustainability science have, in many ways, enhanced recognition across academic, civil, policy and business spheres that humans and nature are inextricably connected. However, in retaining substantialist assumptions where ‘social’ and ‘ecological’ refer to different classes of entity that interact, coupled systems perspectives insist on the inextricability of humans and nature in theory, while requiring researchers to extricate them in practice – thus inadvertently reproducing the separation they seek to repair. Consequently, sustainability researchers are increasingly drawing on scholarship from the ‘relational turn’ in the humanities and the social sciences to propose a paradigm shift for sustainability science: away from focusing on interactions between entities, towards emphasizing continually unfolding processes and relations. Yet there remains widespread uncertainty about the origins, promises and challenges of using relational approaches. In this paper, we identify four themes in relational thinking – continually unfolding processes; embodied experience; reconstructing language and concepts; and ethics/practices of care – and highlight the ways in which these are being drawn on in sustainability science. We conclude by critically discussing how relational approaches might contribute to (i) a paradigm shift in sustainability science, and (ii) transformations towards sustainability. Relational approaches foster more dynamic, holistic accounts of human-nature connectedness; more situated and diverse knowledges for decision-making; and new domains and methods of intervention that nurture relationships in place and practice.