Genocide has been a central topic of current politics several times in the last two decades, especially over Bosnia and Rwanda. Its history has also been a topic of controversy, in countries such as Germany, Japan, and Turkey over murderous Violence in the two world wars, and in North America and Australia over earlier violence against the indigenous peoples. The Spectre of the archetypal genocide, the Nazi Holocaust, stalks twenty first century relations between Israelis and Palestinians. In many other places in the today’s World, allegations of genocide are made and, almost invariably, disputed. Few ideas are as important, but in few cases are the meaning and relevance of a key idea less clearly agreed. The new international tribunals established for the Yugoslav and Rwandan cases have produced important cases that have been analysed, and historical research has fanned out from the Holocaust to many other episodes. An effort has been made to show how conceptual arguments are related to historical cases and contemporary disputes.Genocide has often been seen as involving murderous tendencies so horrible and irrational as to be both utterly exceptional and virtually inexplicable.