In this article we argue that organizations and organizing activities lie at the very heart of the European integration process. Cross-pillar issues require an analytical framework that allows one to study the interplay between the market and security spheres of European integration, including how supranational and intergovernmental actors, private and public, interact with each other. By using sociological institutionalism and its notion of how organizations are institutionalized, we analyse the organizational complexity in the multifaceted policy area of armaments, without losing theoretical clarity.