Chemical air pollution in Europe has been tackled by multiple institutions, in particular the Convention on Long Range Transboundary Air Pollution to Improve Air Quality (CLRTAP) and European Union air pollution policy. The two regimes differ in terms of membership and policymaking capacity which has, over the decades, resulted in significant interplay and the formation of linkages between them that has served to shape both institutions. Additionally, they have pushed each other toward increasingly stringent pollution targets, encouraged shared research and development of air pollution science, and have filled gaps in each other’s policies.