The authors explore the definition of Security sector reform (SSR) as it has emerged in the international community. The makeup of the security sector is examined, principles are identified for implementing SSR, and outcomes SSR is intended to produce are specified. Supporting case studies assess specific SSR programs. The authors conclude that those conducting SSR programs must understand and continually revisit the policy goals of SSR programs so as to develop concepts that support a transitional process that moves forward over time. State actors must acknowledge and often accommodate nonstate security actors more effectively in SSR planning and implementation, while recognizing both the advantages and the risks of collaborating with such actors. The authors also note the need for more flexible and better integrated funding processes. (Originally published by the Strategic Studies Institute.)