For decades, students have been taught that Zimbardo’s infamous Stanford Prison Experiment, where perfectly decent young people were transformed into brutal guards or compliant prisoners in a matter of days, demonstrated the power of situations to determine behaviour. But, more recently, new evidence showing that the researchers were not neutral observers but rather active participants encouraging guard brutality, has led to some psychologists rejecting the study.

Professors Haslam and Reicher take a different view. Using the new evidence about researcher involvement, they move beyond Zimbardo to construct a new, more powerful, and more worrying, explanation of the guards’ brutality.