There is a common intuition that genocide is qualitatively distinct from, and much worse than, mass murder. If we concentrate on the most obvious differences between genocidal killing and other cases of mass murder it is difficult to see why this should be the case. I argue that many cases of genocide involve not merely individual evil but a form of collective action manifesting a collective evil will. It is this that explains the moral distinctiveness of genocide. My view contrasts with one put forward by Claudia Card, though we both agree that the notion of ‘‘social death’’ plays a significant role here.