Genocide, crimes against humanity, and the worst war crimes are possible only when the state or other organizations mobilize and coordinate the efforts of many people. Responsibility for mass atrocity is therefore always widely shared, often by thousands. Yet criminal law, with its liberal underpinnings, insists on blaming particular individuals for isolated acts. Is such law therefore constitutionally unable to make any sense of the most catastrophic conflagrations of our time? Drawing on the experience of several recent prosecutions (both national and international), this book trenchantly diagnoses law’s limits at such times and offers a spirited defense of its moral and intellectual resources for meeting the vexing challenge of holding anyone criminally accountable for mass atrocity. Just as today’s war criminals develop new methods of eluding law’s historic grasp, so criminal law flexibly devises novel responses to their stratagems. Mark Osiel examines several such recent legal innovations in international jurisprudence and proposes still others.