In the early morning hours of Sunday, August 14, 1971, police cars in the small city of Palo Alto, California, were dispatched to the homes of 12 young men. Uniformed officers knocked on their doors and notified the men that they were being charged with armed robbery and burglary. They were read their rights, searched, handcuffed, and put in the back of a squad car. Each was taken to the police station, where he was summarily processed: photographed, fingerprinted, and led to a holding cell. These dozen men were then transferred to prison, where they were to be incarcerated together for 14 days under the watchful eye of the warden and a rotating cast of 12 young prison guards.

Thus began a landmark experiment that offered scholars a remarkable window on the socializing effects of prison. The experimental protocol was fairly straightforward. Twenty-four research subjects, all healthy and normal college-aged men, had been randomly assigned to play the part of either a prisoner or a prison guard. For two weeks, these men would live full time (in the case of the inmates) or work long shifts (in the case of the guards) in a simulated prison that had been carefully constructed in the basement of a building at Stanford University.