The purpose of this book is to assess the existing explanations of Adolf Eichmann's perpetrator behaviour. These include Eichmann as a monster of abnormal personality, Arendt's influential and controversial claim that Eichmann was entirely normal but devoid of capacity for moral reasoning, and Stangneth's and Cesarani's characterisation of Eichmann as an eliminationist antisemite. Arguments against these explanations are presented and the book argues that Eichmann was entirely normal not in the cognitive sense of limited moral awareness and poor appreciation of the consequences of his actions but in the sense of optimisation of his own outcomes in material, social and psychological terms regardless of the cost to others. This new argument is supported by reference to the social psychological experiments of Milgram on obedience to immoral authority and Zimbardo on the influence of role on behaviour, by reference to Browning's research on the perpetrator behaviour of a German police reserve battalion in Poland, and by reference to research on Einsatzgruppen commanders.