In this international project, we investigate the psychological mechanisms explaining radical group behaviour. Perpetrators of group-based violence like hooligans, rioters, or terrorists are often portrayed as either mad or bad. However we argue that any group has the potential to resort to radical behaviour under the “right” conditions. We propose two key factors in this regard. Firstly, a sense of low group efficacy or political power in combination with local social support can promote radicalization. Secondly, threats to the group’s standing in the social hierarchy can evoke contempt, also prompting radical action. Finally we consider interventions designed to defuse radicalization.