There is no authoritative catalogue of principles that set expectations for military members and their commanders operating in what is presumed to be a postconflict space – where residual armed conflict is possible and return to “peace” is uncertain. There is no “Lieber Code” or general regulation imposed on troops to guide their conduct, or from which to deduce and formalize Rules of Engagement (ROE), relative to the “enemy” during the transition from active warfare to conditions of peace and reconciliation. This chapter suggests that such principles are a critical practical necessity for a post bellum transition period and can be understood when stimulated by an unexpected source: criminal law. The military’s post bellum ROE should be based on certain values justified by its unique circumstances: justification, due care, forethought, moderation, nonarbitrariness, self-restraint, and accountability. These values parallel those shaping criminal justice prosecution decisions in military law and are compatible with the jus in bello principles of distinction, humanity, proportionality, and military necessity.