How can conflict-prone countries ensure better delivery of security and justice services? How can they establish structures and mechanisms which will ensure effective and accountable security and justice institutions? Although there has been significant work undertaken over the past decade in a number of security and justice reform programmes, this landmark publication fills a void. The OECD DAC Handbook on Security System Reform: Supporting Security and Justice provides guidance to operationalise the 2005 DAC Guidelines, Security System Reform and Governance, and closes the gap between policy and practice. It largely follows the external assistance programme cycle and contains valuable tools to help encourage a dialogue on security and justice issues and to support a security system reform (SSR) process through the assessment, design and implementation phases. It also provides new guidance on monitoring, review and evaluation of SSR programmes, and highlights how to ensure greater coherence across the different actors and departments engaged in SSR. This work is aimed not only at development practitioners but also defence and diplomatic personnel working to support security and justice reform. The challenge now for the OECD DAC's Network on Conflict, Peace and Development Co-operation (CPDC) is to ensure that the SSR Handbook is implemented at field level. After all, security is fundamental to people's livelihoods, reducing poverty and achieving the Millennium Development Goals.