There have been clear calls for enhanced international cooperation to meet the environmental, economic and criminal challenges of transnational environmental crime (TEC), defined here to include illegal wildlife trade, timber trafficking and the black market in ozone-depleting substances. In the absence of an overarching international or transnational environmental crime legal framework, institutional settings are characterized by regime density and complexity amid a growing number of actors across related but distinct institutional settings. Scholars of international cooperation have worried that this kind of complexity leads to legal indeterminacy, normative ambiguity and regulatory uncertainty that will make cooperation more difficult. In the TEC sphere, these propositions remain under-researched and untested. This article sketches the contours of a study that would bring some conceptual and empirical clarity to these issues. In doing so, it outlines the constitutive elements of the TEC regime complex and the nature of institutional interplay between and among those elements.