Security sector reform (SSR) is widely recognised as key to conflict prevention, peace-building, sustainable development and democratisation. SSR has gained most practical relevance in the context of post-conflict reconstruction of so-called 'failed states' and states emerging from violent internal or inter-state conflict. As this volume shows, almost all states need to reform their security sectors to a greater or lesser extent, according to the specific security, political and socio-economic contexts, as well as in response to the new security challenges resulting from globalisation and post-9/11 developments. Contributions from academics and practitioners elaborate on both the conceptual underpinnings and the practical realities of security sector reform and - a crucial aspect of post-conflict peace-building - security sector reconstruction.