A compelling argument among scholars of genocide reflects the gradual development of the field beyond its point of origin, the Nazi murder of Europe’s Jews. The questions include whether and how different episodes of mass killing should be seen in a common frame; how such a development changes understanding of the Holocaust; and how historical interpretation and modern political argument intertwine, not least over Israel and anti-semitism. Martin Shaw, both participant and observer in this debate, presents an overview of its core issues.