Despite promises made by the international community after the Holocaust to “never again” allow genocide, war crimes, and crimes against humanity to be committed, these “atrocity crimes” have been perpetrated again and again. Today—from Syria and South Sudan to Myanmar and Yemen—such catastrophes still rage around the world, and many more may erupt. This is therefore a crucial time to consider new initiatives to address existing and future humanitarian crises. In addition to political, normative, and technological advancements, novel legal developments in the United States hold great potential to help address atrocity crimes. Two such pieces of legislation—the Syrian War Crimes Accountability Act and the Elie Wiesel Genocide and Atrocities Prevention Act—recently became law in the United States. These landmark acts unprecedentedly enshrine “atrocity prevention” and define “transitional justice” in U.S. law. In addition, for the first time, one of the acts refers to the Atrocities Prevention Board—an interagency body established by executive order—in a non-appropriations law, endowing this entity (and its successor) with greater congressional support and legitimacy. Amid an era in the United States that is more polarized than at any time since the Civil War, that each law garnered overwhelming support from both Democratic and Republican officials demonstrates that Americans can still agree on at least some basic principles. This Article provides the first comprehensive analysis of these groundbreaking laws and how they relate to other scholars’ and my own studies on atrocity prevention and transitional justice.