The BBC Prison Study explores the social and psychological consequences of putting people in groups of unequal power. It examines when people accept inequality and when they challenge it. These findings have changed our basic understanding of how groups and power work. In this program, Alex Haslam and Steve Reicher tell the story of the largest field study in social psychology for over 30 years, using original illustrative film from the BBC series. As well as documenting their study, Haslam and Reicher look at social identity and its implications, the ethics of the study, their sources of data, and comparisons with the Stanford Prison Study.