This volume originated as an international conference on genocide organized by Robert Gellately and Ben Kiernan. The conference was supported by the Harry Frank Guggenheim Foundation and held in Barcelona, Spain, in December 2000. Some of the essays published in this volume were presented at that conference, and those that were have been revised and sometimes also greatly expanded. In addition, we solicited a number of essays to broaden the picture and the discussion of genocide and mass murder in the modern world. This entire project could not have gotten off the ground without the support of the Harry Frank Guggenheim Foundation, and we particularly want to thank its two leading lights, Karen Colvard and James Hester. Five anonymous readers of the manuscript for Cambridge University Press made many very helpful suggestions for the improvement of the manuscript, and we wish to thank them as well. It is our hope that this volume will be useful in the classroom and that it stimulates further reflection about and research into this deeply troubling topic.