The U.S. military Standing Rules of Engagement (SROE) restrict the use of force in armed conflict to either self-defense or “mission-specific” rules of engagement, which refer to the use of force against members of enemy armed forces or organized armed groups that have been “declared hostile.” This bifurcation of authority works well in an international armed conflict, where the enemy force is uniformed and easily distinguished. In these circumstances, the overwhelming number of engagements are against identified hostile forces. In many non-international armed conflicts, however, combatants actively attempt to camouflage their status, and U.S. forces find themselves engaging enemy forces under a self-defense framework. This creates problems. Consider, for example, a situation where three individuals of unknown affiliation launch an attack against a U.S. military convoy in Afghanistan. After a short engagement, the attackers get in a van and speed away from the attack site. The U.S. convoy is disabled, but an unmanned aerial vehicle tracks the van as it retreats into the desert. Thirty minutes later an AH-64 Apache attack helicopter arrives on scene above the still-retreating van. Can the Apache attack the vehicle? The van is retreating and poses no threat, thus self-defense principles would not allow for the use of force, despite the fact that the occupants are clearly directly participating in hostilities. This chapter addresses three questions: Why are the SROE drafted in this manner? What is the basis in the law for the SROE’s approach to self-defense? What are the problems presented by this approach?