This Introduction to Volume I of The Cambridge World History of Genocide, which covers the ancient, medieval, and early modern worlds, raises questions about the nature of premodern genocide, about the meaning of genocide and genocidal intent in the premodern era, and about both perpetrators and victim groups, and about the scale, techniques, and ideologies of genocide in that long historical period in comparison to those of genocides committed in modern times. The chapter considers whether or not genocide can be considered a ‘transhistorical phenomenon’. It also asks whether mass violence in the pre-modern and early modern periods occurred in a different moral context than that of modern times, presenting some differing views on this question. Finally the chapter introduces the substantive chapters of the volume, and how they variously examine material, political, sociocultural, and ideological factors that contributed to premodern outbreaks of genocide, as well as noting some changes over time from prehistory to the early modern era.