While the body of environmental governance research (EGR) continues to grow, it does not appear to become more coherent or cumulable. A lack of knowledge cumulation—defined as the systematic building on previous knowledge by broadening, deepening, contextualizing, questioning or rejecting existing theories and empirical evidence—may hinder both scientific progress and policy relevance. In the interdisciplinary field of EGR, the cumulation of knowledge faces a number of challenges, including epistemological discrepancies; interdisciplinary plurality of concepts, theories, methods and research questions; and an academic incentive system that prioritizes novelty and originality over sustained engagement with prior research. For the first time in EGR, this Special Issue on Knowledge Cumulation in Environmental Governance Research conceptually and empirically explores (a) how knowledge cumulation relates to interdisciplinarity, transdisciplinarity, epistemic justice, action orientation, and policy relevance; (b) how the degree of knowledge cumulation in the field can be assessed, and with what results; (c) which methods support knowledge cumulation; and (d) what generally hinders knowledge cumulation, and how these obstacles can be overcome. The findings are manifold. Within and across several subfields of EGR, epistemological positions, research questions, understandings of key concepts, theories, methods, and author networks prove to be highly fragmented. Structural academic incentives, such as the emphasis on novelty, further inhibit knowledge cumulation. At the same time, interdisciplinary knowledge integration, dialogue and collaboration across knowledge holders and epistemic communities, and research practices and publication formats designed to facilitate knowledge cumulation, offer promising avenues to address the challenges in EGR.