Despite widespread State acceptance of the international law governing military use of force across the spectrum of operations, the humanitarian reality in today's armed conflicts and other situations of violence worldwide is troubling. The structure and incentives of armed forces dictate the need to more systematically integrate that law into operational practice. However, treaty and customary international law is not easily translated into coherent operational guidance and rules of engagement (RoE), a problem that is exacerbated by differences of language and perspective between the armed forces and neutral humanitarian actors with a stake in the law's implementation. The author examines the operative language of RoE with a view to facilitating the work of accurately integrating relevant law of armed conflict and human rights law norms. The analysis highlights three crucial debates surrounding the use of military force and their practical consequences for operations: the dividing line between the conduct of hostilities and law enforcement frameworks, the definition of membership in an organized armed group for the purpose of lethal targeting, and the debate surrounding civilian direct participation in hostilities and the consequent loss of protection against direct attack.