When is it lawful for a nation to go to war and, notwithstanding this question, how may a war be lawfully fought? Where do these two questions come from, and how are they to be answered? The current conflicts in Ukraine and Gaza have re-ignited much interest in that subset of international law that governs the conduct of warfare. Ever since the attacks of September 11, 2001 and the subsequent debates over military tribunals for accused terrorists, the combatant status of captured Taliban fighters and Al Qaeda members, and the proper treatment of detainees, the laws and customs governing armed conflict and the conduct of military operations have received attention perhaps unprecedented since the Nuremberg and Tokyo war crimes trials after WWII. This course will address these topics, as well as: the nature of modern warfare and its impact on the on-going development of the laws of armed conflict; the Just War tradition; international law and custom governing warfare, military operations, and humanitarian intervention.