The growing literature about linkages between international institutions remains littered with proposed taxonomies. Most of these taxonomies are conceptual, rather than empirically driven, remaining too vague to offer guidance for empirical research regarding linkages as possible avenues of influence across international institutions. This article argues that institutional linkages are potential causal pathways by which policy making and implementation are influenced. It supplements concepts of structural governance linkages, which are common in the existing literature, with attention to agent-oriented actor linkages. The article offers a typology of governance and actor linkages that can be operationalized in empirical research. It discusses governance and actor linkages between policy making within the Convention on Long-Range Transboundary Air Pollution and the European Union. The paper argues that research on international environmental cooperation would benefit from greater empirical attention to linkages in a context of a multitude of connected governance and actor linkages.