| The need to achieve stability and security in Europe has been a core motivation for European Union actors in their decision in favour of enlargement, calling for new measures to advance the enlargement process. EU leaders have often justified changes to the existing enlargement strategy by making reference to threats to security in Europe and by claiming that eastern enlargement could be the way to attain peace and security in Europe. Never has EU enlargement been so frequently connected with security debates.The overall effect of security concerns on the enlargement process, however, has not been adequately analysed in previous studies of EU enlargement; enlargement policy has largely been explained from economic and commercial viewpoints.This article explores the role of security concerns in EU enlargement-'security' that does not necessarily come in the military form, but in what I refer to as a 'speech act', drawing on insights from the Copenhagen School of security studies.The article comprises (1) a conceptual framework to consider how 'security' as 'speech act' (or the 'securitization' approach) can explain the enlargement process, (2) three case studies of security influences in the context of EU enlargement, and (3) conclusions on when and how security has mattered in the EU enlargement process |