The International Criminal Court (ICC) is now operational. What is the meaning of this innovation in global governance? Most concretely, the ICC will mean prosecution and jail time for some individuals who commit war crimes, crimes against humanity, or genocide, as defined in international law. In a larger sense, though, what role will this institution play in bringing to bear the rule of law in the context of war? The answer depends not just on the details and limitations of the first few cases that will be heard by the new court, but on the long-term institutionalization of this supranational institution with the power to punish some of the world’s most abhorrent crimes.