In this paper, I offer a general defense of what I call “ethical vigilantism” and argue that it provides the basis for universal jurisdiction and the legitimacy of international criminal law. Following David Luban, I argue that any entity exercising “vigilante jurisdiction” would have to bootstrap itself into legitimacy by delivering high-quality natural justice. International criminal law will have to be vigilantism, in my view, as long as we find it undesirable to enter the world-state to achieve the requisite political authorization for its enforcement.