The chapter provides testimonies of individuals who took part in a genocidal process in order to understand how mass atrocities can take shape across different human societies. Through the analyses of interviews conducted with former genocide perpetrators in Rwanda and in Cambodia, it appears that many of them reported that they participated because they simply followed orders. It thus suggests that obedience to orders strongly influences individual actions during a war or a genocide. The chapter also highlights the key role of other forms of social influence, such as conformity to a group and compliance. However, the interviews reveal that complex additional factors have influenced former perpetrators in their actions, such as elements of coercion, the fear for one’s own life, and hateful propaganda. This chapter illuminatesthe many reasons that can lead a human to perpetrate evil acts.