Psychology is the scientific study of human and animal behavior and mental processes. There are two main types of psychology: research psychology, which studies theories and conducts experiments to understand why things happen; and applied psychology, which focuses on how to use research findings in real-world settings like NASA. Some key fields of psychology include clinical, educational, child, environmental, industrial, engineering, and experimental psychology. Important early psychologists include Darwin, Wundt, James, Freud, Galton, Pavlov, Watson, and Skinner. Their work established foundations in evolutionary theory, introspection, psychoanalysis, behaviorism, and conditioning. Major approaches to psychology include neurobiological, behavioral, humanistic, psychoanalytical,