The purpose of this study is to explain how and why the concept of security sector reform (SSR) has emerged and been integrated in the European Union (EU). The study has a constructivist theoretical framework and also investigates the applicability of the norm life cycle model in relation to SSR. The findings of this study indicate that SSR has emerged as a response to various world-events, in the context of a “human security” agenda, and due to a call for an integrated approach between security and development. The findings also suggest that actors promoting SSR may have been motivated by reasons related to esteem, as well as to their own security and well-being. Moreover, the findings indicate that SSR is only in the beginning of a norm life cycle; and if it is to move forward in the process it needs to become more straightforward, as well as coherently defined and integrated within the various EU bodies. Furthermore, the study makes a suggestion for complementing the theoretical model of the norm life cycle by adding a stage concerned with the practice of norms.