The American Psychological Association (APA) is the main professional organization of psychologists in the United States, and the largest psychological association in the world. It has over 157,000 members, including scientists, educators, clinicians, consultants, and students. It has 54 divisions, which function as interest groups for different subspecialties of psychology or topical areas. The APA has an annual budget of around $125 million.

A psychologist is a professional who practices psychology and studies mental states, perceptual, cognitive, emotional, and social processes and behavior. Their work often involves the experimentation, observation, and interpretation of how individuals relate to each other and to their environments.