The chapter reviews literature on the political impact of the EU’s interaction with international institutions and makes a plea to keep a two way street open, that is, to employ both inside-out and outside-in perspectives. The review of inside-out perspectives highlights how analysts have made important advances within this line of research that branches out into foci such as actorness, normative power, effective multilateralism and performance studies. Given that all foci also imply weaknesses, outside-in perspectives are also considered, using the English School theory of fundamental institutions as a guide. This enables a focus on existing research showing how fundamental institutions, such as diplomacy, great powers, balance of power and international law, have an impact on the EU. Finally, the chapter considers options for synthesizing multiple research agandas, drawing on the agent-structure problematique, subjectivist-objectivist perspectives and temporal perspectives. It is argued that synthesizing research is an attractive tool to bridge the many islands in the wide archipelago of existing studies.