How can we comprehend the socio-political processes that give rise to extreme violence, ethnic cleansing or genocide? A major breakthrough in comparative analysis, Purify and Destroy demonstrates that it is indeed possible to compare the Holocaust, the Rwandan genocide and ethnic cleansing in Bosnia-Hercegovina while respecting the specificities of each. Based on the essential distinction between massacre and genocide, Purify and Destroy identifies the main steps of a general process of destruction, rational and irrational, born of what Semelin terms 'delusional rationality', responding to fears, resentments and utopias, and re-modelling the social body by eliminating 'the enemy'. The main stages that can lead to a genocidal process, with ordinary people becoming perpetrators, are also identified.