Arendt’s engagement with the Eichmann trial raises questions that lie at the theoretical heart of international criminal justice. Do criminal trials of atrocity crimes (“core crimes”) differ in their aims from trials for ordinary domestic law crimes? Does it even make sense to try individuals for collective crimes? What is the point of courts jumping into the political maelstrom of mass violence? This chapter addresses these questions. It examines Arendt’s defense of the Eichmann trial against charges of unfairness and illegitimacy. It addresses Antony Duff’s argument that the moral community of “humanity” has no authority to stage criminal trials, as well as Martti Koskenniemi’s critique of Arendt’s individualist focus. Arendt rejected the concept of collective criminal guilt, although she endorsed a concept of collective political responsibility; the chapter analyzes this distinction. An additional question is whether Arendt’s thinking sheds light on the modern practices of international criminal law. Here, the verdict is mixed. Arendt strongly objected to the political and pedagogical aims of criminal trials, which I argue is a mistake on her part, even on her own terms. The radical ambitions of international criminal justice – to save history against inevitable future denialism, and to demystify extreme political violence – are actually Arendt’s as well, whether or not she recognized it.