["JCMS: Journal of Common Market Studies, EarlyView. ", "\nAbstract\nThis article examines the institutional design of industrial defence co‐operation in Europe, based on a study of the Organisation for Joint Armament Cooperation (OCCAr). At the heart of the agency's mandate lies the global balance rule, intended to overcome the inefficiencies of juste retour by ensuring long‐term equity between participants across multiple programmes. Building on an economic reading of OCCAr's founding texts and management procedures, we propose a conceptual model, from which two working hypotheses are derived. First, that existing arrangements may not always prevent larger states from primarily securing higher value industrial activities, potentially limiting the prospects for smaller partners willing to integrate the European Defence Technological and Industrial Base. Second, that participants could in practice display a preference for short‐term national interests, which may in turn undermine the long‐term equilibrium initially envisaged. These hypotheses are tested through a qualitative case study of the A400M programme, which remains OCCAr's flagship project to date. Findings suggest that although OCCAr introduces innovative institutional mechanisms, state practices can nuance the theoretical framework's range. A comparison with competing programmes such as the C‐130J and C‐390 illustrates how different institutional settings shape industrial organisation and strategic outcomes."]