This article investigates how and to what extent the current management of inter-institutional relationships within International Environmental Governance (‘interplay management’) contributes to Environmental Policy Integration (EPI), and identifies options for enhancing EPI among international institutions. To this end, it first develops a framework for the systematic analysis and assessment of interplay management as a means for achieving ‘strong’ EPI, distinguishing four levels and two principal modes of management. On this basis, the article assesses the current contribution of International Environmental Governance to advancing EPI as regards three categories of institutional interaction. The analysis demonstrates the need to fit interplay management to the particular governance conditions of varying interaction situations and highlights the lack of systematic and consistent support for EPI among international institutions. Options to improve this situation include in particular promoting inter-institutional learning and assistance for the benefit of environmental institutions as well as ensuring consideration of and respect for environmental requirements. Adapting the statutes and mandates of individual institutions and developing suitable guidance under general international (environmental) law have the highest potential for implementing these options. In contrast, joint management initiatives and a strengthened international environmental organisation have a much more limited, supplementary potential.