This paper explores the definition of SSR as it has emerged in the international community. It examines the makeup of the security sector, identifies emergent principles for implementing SSR in the community of practice and specifies the outcomes that SSR is designed to produce. Supporting case studies of Haiti, Liberia, and Kosovo assess the impact of SSR programs on host nation security sectors. The authors conclude that those conducting SSR programs must understand and continually revisit the policy goals of SSR programs, to develop concepts that support a transitional process that moves forward over time. They also identify a need for rebalancing resources committed to SSR, especially since justice and civil law enforcement typically are undersourced as elements of SSR. Lastly, the authors cite the need for more flexible and better integrated funding processes to support SSR activities within the U.S. Government.