The Stanford prison experiment (SPE) was a psychological experiment conducted in the summer of 1971. It was a two-week simulation of a prison environment that examined the effects of situational variables on participants' reactions and behaviours. Stanford University psychology professor Philip Zimbardo led the research team who administered the study.

SPE has been referenced and critiqued as one of the most unethical psychology experiments in history. The harm inflicted on the participants prompted universities worldwide to improve their ethics requirements for human subjects of experiments to prevent them from being similarly harmed. Other researchers have found it difficult to reproduce the study, especially given those constraints.

Critics have described the study as unscientific and fraudulent.