This chapter applies the social psychological theory to the forensically challenging task of explaining genocide. Forensic psychological practitioners are rarely faced with the dilemmas and realities that are faced by victims of extreme trauma, or survivors of ethnic cleansing, torture or genocide. Genocides are not spontaneous events; a long process of societal and psychological change is needed first. Genocides are perpetrated in times of economic hardship and rapid social change. In this context, one group is stigmatized and scapegoated: designated as guilty of the bad times and experienced uncertainties. In such situations, there may be no apparent, real conflict, but long-lasting animosity towards an out-group perceived as a threat to the wellbeing of one's own group. Social organizations and institutions spread ideology to justify stigmatizing and discrimination of designated social groups. After societal and psychological preparations, genocides are triggered by mostly symbolic events, used as excuses to begin mass killings.