Donors increasingly recognize the important role that local/non-state actors often play in the provision of justice and security services in many of the world's fragile and (post-)conflict countries. Despite this recognition, it is proving challenging to include such actors in support for justice and security development programmes. With a view to improving practice in this field, the Clingendael Institute's Conflict Research Unit has investigated conceptual, policy and practical opportunities and challenges for including local/non-state security and justice networks in security and justice programming. The present report is the synthesis of this multi-annual research project. It distills the available information on how to effectively support local/non-state security and justice actors from the project, which included a desk-study, three case-studies (Burundi, South Kivu in Eastern Democratic Republic of Congo, and Colombia), and an expert brainstorm meeting. It concludes that supporting such actors is possible, and might generate positive effects for human security in the short to intermediate term, but that such support requires: a willingness from donors to take risks; a focus on ensuring linkages between local/non-state actors and the security and justice agencies of the central state; communication, advocacy and knowledge management strategies; flexible and innovative funding mechanisms; and a focus on accountability mechanisms.