Abstract While the Treaty of Rome allowed member states to establish policies governing the trade in and production of armaments at the national level, the European Union (EU) has gradually been expanding its influence in defense industry matters. This article traces the history of EU involvement in defense industrial policy, with an emphasis on events over the past decade. One significant finding is that the European Commission and Parliament have played key roles in expanding the EU's policy-making machinery to include defense industrial matters, while the Council of Ministers has tried to resist such actions. A second important conclusion is that the concept of spillover is particularly appropriate in describing how and why the EU's policy-making has expanded to include defense industrial policies.