It is a widely shared belief that genocide – the ‘crime of crimes’– is more morally significant than ‘mere’ large-scale mass murder. Various attempts have been made to capture that separate evil of genocide: some have attempted to locate it in damage done to individuals, while others have focused upon the harm done to collectives. In this article, I offer a third, neglected, option. Genocide damages humankind: it is here that the difference is to be found. I show that this understanding has a venerable legal history, and argue that it has the significant benefits of legitimising intervention and justifying universal jurisdiction.