Genocide involves state-organized destruction of a people because of what political scientist R. J. Rummel calls "their indelible group membership (race, ethnicity, religion, language)." Nazi Germany's destruction of European Jewry was clearly genocide; however, was the Holocaust unique?

Arguments for the Holocaust's uniqueness do not depend primarily on the number of Jewish victims or the way in which they were killed. Rather, as scholar Steven T. Katz maintains, the uniqueness claim rests on "the fact that never before has a state set out, as a matter of intentional principle and actualized policy, to annihilate physically every man, woman, and child belonging to a specific people....Only in the case of Jewry under the Third Reich was such all-inclusive, noncompromising, unmitigated murder intended."

The uniqueness claim sparks debate. Some scholars contend, for example, that Nazi Germany's targeting of the Sinti and Roma (Gypsies) did not differ substantially from the fate intended for the Jews. Others fear that the uniqueness claim banishes other genocides to undeserved second-class status. Inquiry about these issues will not stop any time soon, but Holocaust scholar Yehuda Bauer, who defends the Holocaust's uniqueness, offers an important reminder: "Events happen because they are possible. If they were possible once, they are possible again. In that sense, the Holocaust is not unique, but a warning for the future."