During wartime a critical legal question involves the scope of authority to choose whether to kill or capture enemy combatants. One view maintains that a combatant is lawfully subject to lethal force wherever the person is found - unless and until the individual offers to surrender. In contrast, this article concludes that important restraints on the use of deadly force were a part of the agreement reached by states and codified in the 1977 First Additional Protocol to the Geneva Conventions. When nations of the world focused their attention on balancing principles of humanity and military necessity, and making higher law, they agreed on two important sets of rules. Under Article 35, states agreed to prohibit the manifestly unnecessary killing of enemy combatants. And, under Article 41, they agreed that combatants who are completely defenceless, at the mercy of enemy forces, shall be considered hors de combat. - including alternative specifications of standards and burdens of proof. Nevertheless, the general constraint - and its key components - should be understood to have a solid foundation in the structure, rules, and practices of modern warfare.