AbstractTransnational governance initiatives increasingly face the problem of regime complexity in which a proliferation of regulatory schemes operate in the same policy domain, supported by varying combinations of public and private actors. The literature suggests that such regime complexity can lead to forum shopping and other self‐interested strategies, which undermine the effectiveness of transnational regulation. Based on the design principles of experimentalist governance, this paper identifies a variety of pathways and mechanisms, which promote productive interactions in regime complexes. We use the case of the EU's Forest Law Enforcement Governance and Trade (FLEGT) initiative, interacting with private certification schemes and public legal timber regulations, including those of third countries such as the US and China, to demonstrate how an increasingly comprehensive transnational regime can be assembled by linking together distinct components of a regime complex. We argue that it is the experimentalist features of this initiative and its regulatory interactions, which accommodate local diversity and foster recursive learning from decentralized implementation experience, that make it possible to build up a flexible and adaptive transnational governance regime from an assemblage of interconnected pieces, even in situations where interests diverge and no hegemon can impose its own will.