The concepts of necessity, imminence, and proportionality play a central part in Daniel Bethlehem’s sixteen proposed principles regulating a state’s use of force against an imminent or actual attack by nonstate actors. While all three are requirements that must be considered in the law of self-defense, their exact content remains somewhat unclear. In this comment, we examine how each one is conceived in Bethlehem’s principles and review the questions that remain unanswered.