This survey course covers the law of armed conflict and customary international law as applied on today’s battlefields. Is there really law in combat? When does the law of war apply? Does it apply to non-State actors? What is a war crime, and who decides? How is proportionality determined? What is the difference between a combatant, a terrorist, and a criminal? Is torture ever lawful? Is targeted killing lawful? What constitutes a cyber attack? What is the jurisdiction of military commissions and why is that a difficult question for Guantánamo? Can a superior’s order constitute a defense to war crime charges? Is indefinite detention lawful? Can the U.S. ever lawfully kill a U.S. citizen in a foreign state with which we are not at war? Such questions are the subject of the course. It is not a philosophy course, nor is it national security law, nor human rights law, although those topics are inextricably related. Our focus is on the law applicable in today’s non-international armed conflict battlefields. Military experience is not required to do well in this course.