Why people do the things they do is an age-old question. However, psychology — the science concerned with behavior, in both human and nonhuman animals — first appeared in the 1870s. Despite its youth, it is a broad discipline, essentially spanning subject matter from biology to sociology. Psychologists have doctoral degrees. They study the intersection of two critical relationships: one between brain function and behavior, and another between the environment and behavior. As scientists, psychologists follow scientific methods, using careful observation, experimentation and analysis. But psychologists also need to be creative in the way they apply scientific findings.

Psychologists frequently are innovators, evolving new approaches from established knowledge to meet the changing needs of people, organizations, and societies. They develop theories and test them through their research. As this research yields new information, these findings become part of the body of knowledge that practitioners call on in their work with clients and patients, as well as with organizations and communities. Psychology is a tremendously varied field. Psychologists conduct both basic and applied research, serve as consultants to communities and organizations, diagnose and treat people, and teach future psychologists and those who will pursue other disciplines. They test intelligence and personality. Many psychologists work as health care providers. They assess behavioral and mental function and well-being, study how human beings relate to each other and also to machines, and work to improve these relationships. And because the United States is undergoing sizable change in its population makeup, psychologists provide important knowledge and skills to help better understand diverse cultures.