The Experiment is a 2002 BBC documentary series in which 15 men are randomly selected to be either "prisoner" or guard, contained in a simulated prison over an eight-day period. Produced by Steve Reicher and Alex Haslam, it presents the findings of what has subsequently become known as the BBC Prison Study. These findings centered around "the social and psychological consequences of putting people in groups of unequal power" and "when people accept inequality and when they challenge it".

The findings of the study were very different from those of the Stanford Prison Experiment. Specifically, (a) there was no evidence of guards conforming "naturally" to the role, and (b) in response to manipulations that served to increase a sense of shared identity amongst the prisoners, over time, they demonstrated increased resistance to the guards' regime. This culminated in a prison breakout on Day 6 of the study that made the regime unworkable. After this, the participants created a "self-governing commune" but this too collapsed due to internal tensions created by those who had organized the earlier breakout. After this, a group of former prisoners and guards conspired to install a new prisoner-guard regime in which they would be the "new guards". Now, however, they wanted to run the system along much harsher lines – akin to those seen in the Stanford study. Signs that this would compromise the well-being of participants led to early termination of the study.

The genesis of the programme was the 1971 Stanford prison experiment carried out by Philip Zimbardo at Stanford University, in which a group of students were recruited to perform the roles of 'prisoner' and 'guard' as a psychological experiment to test how human beings conform to roles. That study was brought to a premature end as a result of the extreme brutality displayed by guards towards prisoners.

This itself was related to the Milgram experiment at Yale University in 1961.

The BBC Experiment was led by psychologists Professor Alex Haslam (University of Queensland) and Professor Steve Reicher (University of St Andrews) who planned and designed the psychological experiment with the series' executive producer Nick Mirsky and producer Gaby Koppel of the BBC. At the time, Reicher was editor of the British Journal of Social Psychology and Haslam was editor-elect of the European Journal of Social Psychology.

Before The Experiment could proceed, the researchers had to secure formal ethical approval from the University of Exeter. This approval was conditional on the BBC putting in place a range of safeguards to protect against psychological damage to the participants. Key safeguards included:

On the first day, the guards arrive at the prison. They are given uniforms and instructions on how to run the prison. Before the prisoners even arrive, the guards have gained a sense of ownership towards the prison.

Next, the prisoners arrive and are immediately ordered to shower and change into uniforms. All their personal items are taken away, even their hair, which is cut off. Prisoners are unhappy with their mistreatment but acknowledge that there is nothing they can do to change their situation. They accept their position, just as the guards have accepted their privilege.