What Is Psychology? A Plain-English Guide

Reference · Understanding Psychology

In brief: Psychology is the scientific study of the mind and behavior. Psychologists research and treat how people think, feel, learn, decide and relate to one another, using systematic observation and experiments rather than intuition alone. In the United States, a licensed psychologist usually holds a doctorate (PhD or PsyD), completes supervised clinical experience and passes a national licensing exam.

What is psychology?

The American Psychological Association (APA), the largest professional organization of psychologists in the United States, defines psychology as “the study of the mind and behavior.” The definition is short, but the territory it covers is enormous: memory, emotion, perception, motivation, personality, relationships, mental illness and the way groups and whole societies behave.

What makes psychology a science rather than a collection of opinions is its method. Psychologists form testable ideas about behavior, gather evidence, measure results and publish their work so that others can check it. Everyday “common sense” about people is often a starting point, but research regularly shows that common sense is incomplete or wrong.

Psychology also has two faces. One is research, which aims to understand how minds work. The other is practice, which applies that knowledge to help individuals, families, schools, workplaces and courts. Many psychologists do both.

What do psychologists study?

At the broadest level, psychologists ask why people do what they do. That question is approached at several levels at once:

• Biological: the brain, nervous system, hormones and genetics that underlie thought and behavior
• Cognitive: attention, memory, language, reasoning and decision-making
• Emotional and motivational: what people feel, what they want, and how those states drive action
• Developmental: how people change from infancy through old age
• Social and cultural: how other people, groups and cultures shape individual thinking and behavior
• Clinical: the causes, assessment and treatment of mental, emotional and behavioral problems

What are the main branches of psychology?

Psychology is divided into many subfields. The APA itself organizes members into dozens of divisions, each devoted to a specialty. The table below covers the major branches most people encounter.

According to the U.S. Bureau of Labor Statistics, psychologists held about 209,400 jobs in 2025. Clinical and counseling psychologists were the largest group (about 81,300), followed by school psychologists (about 64,000); industrial-organizational psychologists were a much smaller group (about 4,000).

What is the difference between a psychologist, a psychiatrist, a counselor and a social worker?

These titles are often used interchangeably, but they describe different training paths and different legal powers. The biggest practical difference is who can prescribe medication.

Psychiatrists are physicians. After medical school they complete four years of psychiatry residency, and they can provide psychotherapy as well as prescribe medication and other medical treatments.

Psychologists hold a doctoral degree. A PhD traditionally emphasizes research and ends with a dissertation, while a PsyD focuses more on clinical practice, according to the Bureau of Labor Statistics. Psychologists treat people mainly through psychotherapy, and many specialize in psychological testing and evaluation.

Counselors and therapists usually hold a master’s degree. “Therapist” is a general description rather than a protected title, so a therapist might be a psychologist, a licensed counselor, a marriage and family therapist or a clinical social worker. Clinical social workers hold a master’s degree in social work and combine therapy with case management and advocacy, as described by the National Alliance on Mental Illness.

Can psychologists prescribe medication?

In most of the United States, no. But a growing number of states allow psychologists with advanced training in psychopharmacology to prescribe certain medications. As of October 2026, nine states have passed such laws: Colorado, Hawaii, Idaho, Illinois, Iowa, Louisiana, New Mexico, Utah and Vermont. Specially trained psychologists can also prescribe within the U.S. Department of Defense, the U.S. Public Health Service and the Indian Health Service.

The two newest laws come with limits. Vermont’s law was signed on April 27, 2026, but eligible psychologists cannot begin prescribing until July 2029. Hawaii’s law, effective July 15, 2026, creates a three-year pilot program at federally qualified health centers on the islands of Hawaii and Kauai, for adults ages 18 to 65 under physician or psychiatrist supervision.

How do you become a licensed psychologist in the US?

Every state and the District of Columbia requires a license for psychologists who practice independently, and licensing is handled by each state’s psychology board. Details differ from state to state, but the path generally looks like this:

• Bachelor’s degree, often in psychology or a related field
• Doctoral degree (PhD or PsyD), typically from an accredited program, which commonly takes several years beyond the bachelor’s
• Supervised experience, usually including a year-long predoctoral internship and, in many states, additional postdoctoral hours; the required total varies by state
• The national licensing exam, the Examination for Professional Practice in Psychology (EPPP)
• State-specific requirements, which in many states include a jurisprudence (law and ethics) exam
• Continuing education to renew the license

The EPPP is developed by the Association of State and Provincial Psychology Boards (ASPPB). Its knowledge section has 225 multiple-choice questions, 175 of them scored, with 4 hours and 15 minutes allowed; boards commonly use a scaled passing score of 500. ASPPB has also been rolling out a second, skills-based section, and its board set a target that the EPPP become one exam with two parts no later than January 1, 2026. Candidates should check with their own state board for current requirements.

How do psychologists do research?

Psychology relies on several research methods, each suited to different questions:

• Experiments randomly assign people to conditions to test cause and effect.
• Correlational studies measure how two things move together, without proving that one causes the other.
• Surveys gather self-reports from large samples.
• Case studies examine one person or a small group in depth.
• Observational studies record behavior in natural settings.
• Brain imaging and physiological measures track what happens in the body during thought and emotion.

The field also checks itself. In 2015 a large team published an attempt to repeat 100 published psychology studies in the journal Science. While about 97% of the original studies reported statistically significant results, only 36% of the replications did. That finding pushed many researchers toward larger samples, pre-registered study plans and more frequent replication.

What are common myths about psychology?

• “We only use 10% of our brains.” This is an urban legend; brain imaging shows activity throughout the brain, as Scientific American has explained.
• “People are either left-brained or right-brained.” Both hemispheres work together on reading, math and creativity; imaging studies do not support a “creative right brain.”
• “Everyone has a learning style, such as visual or auditory.” Studies have found little support for the idea that teaching to a preferred sensory style improves learning.
• “Psychology is just common sense.” Many intuitive beliefs about memory, persuasion and behavior turn out to be wrong when tested.
• “All psychologists are therapists.” Many psychologists work in research, education, business, law or government and never see clients.
• “A psychologist and a psychiatrist are the same thing.” They have different degrees, and in most states only the psychiatrist can prescribe.

Why does psychology matter for understanding news and politics?

Politics is, in large part, human behavior on a national stage. Psychology offers tools for understanding why voters stay loyal to a leader, why people judge others by the company they keep, and why group membership can shape opinions as strongly as facts do. The specialty that studies these questions is covered in our guide What Is Political Psychology?.

These ideas also run through the site’s commentary. For examples, see the analysis of conformity and political opinions in group chats and the psychology of Trump supporters from 2016 to 2026. For how the field developed, read the history of psychology, and for more commentary, visit the psychology hub.

Key takeaways

• Psychology is the scientific study of the mind and behavior, spanning biology, thinking, emotion, development and social life.
• Major branches include clinical, counseling, cognitive, developmental, social, personality, biological, industrial-organizational, health, forensic and political psychology.
• Psychologists hold doctorates and treat mainly through therapy and testing; psychiatrists are physicians who can prescribe medication.
• As of October 2026, nine states have laws allowing specially trained psychologists to prescribe, though Vermont’s does not take effect until 2029 and Hawaii’s is a limited pilot.
• US licensure requires a doctorate, supervised experience, the national EPPP exam and any additional state requirements.

More in Understanding Psychology

• A Brief History of Psychology: From Philosophy to Science
• Milestones That Changed the Psychology Profession
• What Is Political Psychology? How the Mind Shapes Politics

Sources

• Psychology (citing the APA definition) — Kingsborough Community College, CUNY
• Psychologists, Occupational Outlook Handbook — U.S. Bureau of Labor Statistics
• What Is Psychiatry? — American Psychiatric Association
• Types of Mental Health Professionals — National Alliance on Mental Illness
• Prescriptive Authority for Psychologists: What Patients and Policymakers Need to Know — ASPPB
• 2 states join in expanding psychologist prescribing authority — Becker’s Behavioral Health
• EPPP FAQ — Oregon Board of Psychology
• ASPPB EPPP (Part 2-Skills) Update — ASPPB
• Report Demonstrates Need for Improved Reproducibility in Psychological Science — Association for Psychological Science
• Five Common Myths about the Brain — Scientific American

Part of the brossi.us reference library, written for readers of Dr. Bart Rossi, PhD. Last reviewed October 2026.