Philip Zimbardo in the context of Discovering Psychology

The Stanford prison experiment (SPE), also referred to as the Zimbardo prison experiment (ZPE), was a controversial psychological experiment performed in August 1971 at Stanford University. It was designed to be a two-week simulation of a prison environment that examined the effects of situational variables on participants' reactions and behaviors. Stanford University psychology professor Philip Zimbardo managed the research team who administered the study. Zimbardo ended the experiment early after realizing the guard participants' abuse of the prisoners had gone too far.

Participants were recruited from the local community through an advertisement in the newspapers offering $15 per day ($119.41 in 2025) to male students who wanted to participate in a "psychological study of prison life". 24 participants were chosen after assessments of psychological stability and then assigned randomly to the role of prisoners or prison guards. Critics have questioned the validity of these methods.Those volunteers selected to be "guards" were given uniforms designed specifically to de-individuate them, and they were instructed to prevent prisoners from escaping. The experiment started officially when "prisoners" were arrested by the real police of Palo Alto. During the next five days, psychological abuse of the prisoners by the "guards" became increasingly brutal. After psychologist Christina Maslach visited to evaluate the conditions, she was troubled to see how study participants were behaving and she confronted Zimbardo. He ended the experiment on the sixth day.

Moral blindness, also known as ethical blindness, is defined as a person's temporary inability to see the ethical aspect of a decision they are making. It is often caused by external factors due to which an individual is unable to see the immoral aspect of their behavior in that particular situation.

While the concept of moral blindness (and more broadly, that of immorality) has its roots in ancient philosophy, the idea of moral blindness became popular after the events of World War II, particularly the Holocaust. This led to more research by psychologists and some surprising findings (notably by Stanley Milgram and Philip Zimbardo) on human behavior in the context of obedience and authority bias.