What does the legal regulation of armed conflict at the beginning of the twenty-first century look like? Is it legally permissible to target anyone, anywhere, with armed drones? Can and should States apply their own human rights standards when they are involved in a multinational operation abroad? When, if ever, would a cyber-operation amount to an armed conflict? Some of these questions come up time and again as we scroll through the daily news feed. They all relate to what we call the "scope of applicability" of the body of law regulating armed conflict – international humanitarian law (IHL) – and its interaction with other legal regimes.