Operational systems engineering is a methodology that identifies the important components of a complex system, analyzes the relationships among those components, and creates models of the system to explore its behavior and possible ways of changing that behavior. In this way it offers quantitative and qualitative techniques to support the design, analysis, and governance of systems of diverse scale and complexity for the delivery of products or services. Many peacebuilding interventions function essentially as the provision of services in response to demands elicited from societies in crisis. At its core, operational systems engineering attempts to understand and manage the supply of services and product in response to such demands. Harnessing Operational Systems Engineering to Support Peacebuilding is the summary of a workshop convened in November 2012 by the Roundtable on Science, Technology, and Peacebuilding of the National Academy of Engineering and the United States Institute of Peace to explore the question When can operational systems engineering, appropriately applied, be a useful tool for improving the elicitation of need, the design, the implementation, and the effectiveness of peacebuilding interventions? The workshop convened experts in conflict prevention, conflict management, postconflict stabilization, and reconstruction along with experts in various fields of operational systems engineering to identify what additional types of nonnumerical systems methods might be available for application to peacebuilding.