This research brings together studies of non-state actors (NSAs) in environmental negotiations, transnational networks, and institutional fragmentation, to shed light on the influence of NSAs on policy-making in regime complexes. It presents a new analytical framework with a series of deductive assumptions about the influence of “multi-forum” NSAs, as compared with “single forum” NSAs. Multi-forum NSAs cover several elements of a regime complex, and are thereby able to follow and potentially influence fragmented institutional processes. Focusing on two cases of fragmented environmental governance—forestry and access to genetic resources—the analysis provides a quantitative (statistics, network analysis) and qualitative (interviews) testing ground for the proposed framework. Because of their considerable material, organizational and ideational resources, and long-term engagement, multi-forum NSAs have greater access to the negotiations and may become central players. The strategies such NSAs adopt can further the integration of regime complexes when they undertake forum linking, or push towards further fragmentation when they undertake forum shopping or forum shifting.