Fifteen years ago, the European Union (EU) launched a Common European Security and Defence Policy (CSDP). Since then, the CSDP has been the focus of a growing body of political and scholarly evaluations. While most commentators have acknowledged shortfalls in European military capabilities, many remain cautiously optimistic about the CSDP’s future. This article uses economic alliance theory to explain why EU member states have failed, so far, to create a potent common defence policy and to evaluate the policy’s future prospects. It demonstrates, through theoretical, case study-based and statistical analysis, that CSDP is more prone to collective action problems than relevant institutional alternatives, and concludes that the best option for Europeans is to refocus attention fully on cooperation within a NATO framework.