Landmark Psychology Experiments

Landmark psychology experiments are the studies that changed how psychologists understand behavior and the mind, and that still appear in almost every introductory textbook. They include Milgram's obedience studies, Asch's conformity experiments, Pavlov's conditioning research, Bandura's Bobo doll study and Harlow's work on attachment in monkeys. Each one revealed something surprising, uncomfortable or hard to ignore about human nature.

These studies are not flawless. Many were carried out before modern ethics rules existed, and several have since faced serious criticism over their methods, their treatment of participants or how their results were reported. Reading them today means holding two ideas at once: appreciating what they taught us, while understanding why research ethics and research methods had to change. That tension is part of what makes them worth studying.

This hub gathers our in-depth guides to the most influential experiments and the theories they shaped. Each guide explains what the researchers did, what they found, how the study has been criticized or replicated, and what psychologists make of it now.

Obedience & Authority

How far will ordinary people go when someone in charge tells them to? In the early 1960s, Stanley Milgram found that most participants in his best-known condition continued to give what they believed were dangerous electric shocks when an experimenter told them to. Our Milgram experiment guide covers the procedure, his many variations, and later critiques. The Stanford prison experiment (1971) is often discussed alongside it, but it is now widely regarded as a flawed demonstration rather than solid evidence, and our guide explains why.

Conformity & Group Influence

We like to think we make up our own minds. Solomon Asch's line-judgment studies showed that many people will sometimes go along with an obviously wrong group answer. Muzafer Sherif's Robbers Cave experiment showed how quickly competition can create hostility between groups, and how shared goals can reduce it. Research on the bystander effect asked why people sometimes fail to help in emergencies, and also shows how a misreported news story shaped a whole research field. For the bigger picture, start with social influence and social psychology.

Learning & Behavior

Some of psychology's oldest experiments asked how behavior is learned. Pavlov's dogs revealed classical conditioning, while Thorndike's puzzle boxes and Skinner's operant chambers led to operant conditioning. Watson and Rayner's Little Albert study tried to show that fear could be conditioned in a human infant. Bandura's Bobo doll experiment showed children imitating aggression they had watched, the basis of social learning theory. Seligman's research on learned helplessness explored what happens when outcomes feel uncontrollable.

Development & the Mind

Experiments on development changed ideas about what children need. Harry Harlow's monkey experiments showed that infant monkeys sought comfort from a soft surrogate rather than just food, supporting attachment theory. Walter Mischel's marshmallow test studied delay of gratification, and later replications have reshaped how its long-term findings are interpreted. Research on cognitive dissonance and the fundamental attribution error revealed predictable patterns in how adults think about themselves and others.

The Researchers Behind the Studies

Behind each experiment is a researcher with a particular question and the methods of their time. Our profiles of figures such as Stanley Milgram, Albert Bandura, Ivan Pavlov and Philip Zimbardo put their work in context. Our list of famous psychologists covers many more.

How Experiments Work

To judge a famous study, it helps to know how experiments are designed. A true experiment manipulates an independent variable, measures a dependent variable, and uses random assignment and control groups to rule out other explanations. Many landmark studies fall short of that standard in some way: small or unrepresentative samples, no control group, or procedures that changed as the study went on. Our guide to research methods in psychology explains these concepts, along with reliability, validity, ethics and the replication crisis.

Ethics and Replication

Several landmark experiments directly prompted modern research ethics. Concerns about deception and distress in obedience research, and about the treatment of participants in medical studies, led to rules requiring ethics review, informed consent, the right to withdraw and full debriefing. Today, studies like Little Albert or the original Milgram procedure would not be approved in their original form.

The replication crisis of the 2010s added a second lens. When researchers attempted to repeat many published findings, a substantial share produced weaker results or none at all. Some classic findings, such as basic conditioning effects and Asch-style conformity, have held up well in many replications. Others, including the long-term predictions of the marshmallow test and some dramatic claims from the Stanford prison experiment, look weaker or more complicated than first reported.

Where to Start

If you're new to the topic, a good path is to begin with the Milgram experiment and the Bobo doll experiment, which show two very different ways that social situations shape behavior. Then read Pavlov's dogs and classical conditioning to see how the science of learning began. Finish with the Stanford prison experiment to practice evaluating a famous study critically. The full list of guides in this section appears below.