This book critically analyzes the European Union’s role in Security Sector Reform (SSR), a topical issue with regards to European security. While the literature on SSR has increased significantly in the past decade, too little remain in the way of comparative analyses of SSR case studies that are geared toward theory development. This collection strives to push the SSR literature in that direction. One key question it focuses on is whether the EU pursues a holistic approach vis-à-vis SSR. Another question the book addresses is why and how the EU activities towards SSR in conflict management, peacebuilding and statebuilding have produced a wide variety of outcomes that range from the failure to reform any or all of the sub-set of security sectors (police, justice, military, etc.) to complete and integrated reform. The volume encompasses all relevant cases of SSR in terms of the financial, human, and political resources involved at the EU level. Cases are drawn from the Balkans (Kosovo; Bosnia-Herzegovina), Africa (Democratic Republic of Congo), the Middle East (Palestinian Territories), Post-Soviet Space (Georgia), and Asia (Aceh, Indonesia). The end product is a welcome contribution to the literature, providing both an empirically and theoretically grounded approach to the study of SSR. This book was originally published as a special issue of European Security.