Standard works on international environmental governance assume single-issue regimes with binding obligations designed to govern the behaviour of states. Yet many of the most pressing global environmental problems, including climate change, forest degradation and biodiversity loss, are governed by an array of mechanisms—legal, non-legal, governmental and non-governmental—in complex arrangements. Examining the combined effects of these international and transnational efforts on domestic or firm policies and practices—the usual targets of such efforts—requires expanding a focus on regime ‘compliance’ and ‘effectiveness’ to ‘influence’ factors from beyond state borders. To facilitate such a move, the authors develop a framework that distinguishes four distinct pathways through which actors and institutions influence domestic policies: international rules; international norms and discourse; creation of, or interventions in, markets; and direct access to domestic policy processes. Propositions are then developed on the conditions under which, and processes through which, actors and institutions affect domestic and firm policies and practices along each pathway. The framework is applied to the case of forest governance, a prototypical example of complex global environmental governance.