Programs for the Disarmament, Demobilization, and Reintegration (DDR) of ex-combatants have become more common as an element in the peacebuilder’s toolkit. They have evolved over the last 15 years, and can interact positively with an ongoing peace process. The literature assessing DDR is reviewed in this paper. Results have not always been positive, however. Despite recognition of the need for a more holistic, integrated approach, there are real challenges in implementing such a complex program in a post-conflict environment. Qualitative studies have highlighted these difficulties, and the few quantitative assessments of the outcomes are mixed. However, understanding of DDR is being advanced by a rich policy literature, together with specific “best practice” studies. Recognition of the importance of a participatory approach, and ownership of the process by the beneficiaries, has added to this understanding. The paper concludes that DDR is set to remain an important tool, and that it is most effective when used flexibly, appropriately, and with the genuine participation of those it is supposed to benefit.