A handful of experiments have shaped psychology more than any others. They are the studies that appear in every introductory textbook, that get debated in lecture halls, and that turn up in conversations far beyond academia. What unites them is not a single topic but a single quality: each one revealed something about human nature that was surprising, uncomfortable, or simply hard to ignore.
Some of these studies asked how far ordinary people will go when an authority figure gives an order. Others showed how easily our judgments bend to fit the group around us, or how children learn aggression simply by watching adults. Still others explored how we form attachments, how we respond to helplessness, and why bystanders sometimes fail to act in an emergency. Together they helped build the foundations of social psychology, the study of learning, and our understanding of attachment.
These experiments are not flawless. Many were carried out before modern ethical standards 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 about behavior, while recognizing why research ethics 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 researchers behind them. Browse them by theme below — from obedience and conformity to learning, development, and the methods that make rigorous research possible. Each guide explains what the study did, what it found, and how psychologists interpret it now.
Obedience & Authority
How far will people go when told to by someone in charge? These studies put obedience and the power of situations to the test.
Conformity & Group Influence
We like to think we make up our own minds. These experiments reveal how powerfully groups shape what we say and do.
The Asch Conformity Experiment
People gave obviously wrong answers just to match the group around them.
The Bystander Effect & Kitty Genovese
Why people often fail to help when others are present to share responsibility.
The Robbers Cave Experiment
How groups form rivalries — and how shared goals can ease conflict between them.
Social Influence
The broader science of how others change our beliefs, choices, and actions.
Learning & Behavior
The classic studies of conditioning and imitation that revealed how behavior is learned, shaped, and reinforced.
The Bobo Doll Experiment
Children imitated aggression they had simply watched an adult perform.
Pavlov's Dogs
The famous study that revealed how reflexes can be conditioned to new cues.
The Little Albert Experiment
A controversial study showing an emotional fear could be conditioned in a child.
Classical Conditioning
The learning principle behind Pavlov's work, explained in depth.
Operant Conditioning
How rewards and consequences shape behavior over time.
Social Learning Theory
The framework Bandura built around learning through observation.
Learned Helplessness
How repeated uncontrollable events can teach a sense of powerlessness.
Development & the Mind
Experiments that reshaped how we understand attachment, self-control, and the inner life of children.
Harlow's Monkey Experiments
Studies of comfort and attachment that challenged ideas about why infants bond.
The Marshmallow Test
The famous study of delayed gratification — and what later research revised.
Cognitive Dissonance
The discomfort of holding conflicting beliefs, and how we resolve it.
Attachment Theory
How early bonds shape relationships across the whole lifespan.
The Fundamental Attribution Error
Why we blame character in others but circumstances in ourselves.
The Researchers Behind the Studies
The psychologists who designed these experiments and shaped the questions the field still asks today.
Stanley Milgram
The social psychologist behind the landmark obedience studies.
Philip Zimbardo
The researcher who ran the Stanford prison experiment.
Solomon Asch
Pioneer of conformity research and the famous line-judgment task.
Albert Bandura
Creator of the Bobo doll study and social learning theory.
Ivan Pavlov
The physiologist whose dogs revealed classical conditioning.
Leon Festinger
The theorist who introduced cognitive dissonance.
Martin Seligman
Known for learned helplessness and later positive psychology.
Jean Piaget
Whose studies of children mapped the stages of cognitive development.
Famous Psychologists
A wider directory of the people who built the field.
How Experiments Work
The methods and disciplines that turn a question about behavior into a testable, repeatable study.
Psychology Research Methods
Experiments, surveys, and the tools researchers use to study behavior.
Social Psychology
The branch behind many of these landmark studies of behavior in groups.
Developmental Psychology
How psychologists study change across infancy, childhood, and beyond.
What Is Psychology?
A complete introduction to the science of mind and behavior.
Frequently Asked Questions
What is a landmark psychology experiment?
A landmark psychology experiment is a study that fundamentally changed how researchers understand the mind or behavior, often by producing surprising results, sparking debate, or shaping the direction of an entire subfield. Classic examples include Milgram's obedience studies, Asch's conformity experiments, and Bandura's Bobo doll study. These experiments are widely taught because of their influence, even when later researchers have questioned their methods or interpretations.
What was the most famous experiment in psychology?
Stanley Milgram's obedience experiments are among the most famous in all of psychology. Conducted at Yale in the early 1960s, they showed that many ordinary people would follow an authority figure's instructions to deliver what they believed were dangerous electric shocks to another person. The findings reshaped how psychologists think about obedience, authority, and personal responsibility.
Why are some classic experiments controversial today?
Many classic studies were conducted before modern ethical standards existed, and some exposed participants to stress, deception, or potential harm without adequate safeguards. Studies like the Stanford prison experiment and the Little Albert experiment are now frequently criticized on ethical grounds, and some have faced questions about their methods and how their results were reported. They remain valuable for understanding both human behavior and how research ethics have evolved.
How do modern ethics rules protect experiment participants?
Today, research involving people must be reviewed by an ethics board, obtain informed consent, minimize potential harm, allow participants to withdraw, and protect confidentiality. Deception is permitted only when justified and is followed by debriefing. These safeguards grew partly in response to concerns raised by some of the very experiments featured on this page. Our guide to psychology research methods explains how studies are designed responsibly.
Keep Exploring the Science of Behavior
These experiments are doorways into the wider field. Once you have seen what they revealed, dig into the branches and methods that grew out of them.