Psychology is the scientific study of behavior and mental processes, examining how these are influenced by an organism's physical state, mental state, and environment. The field encompasses various historical perspectives such as structuralism, functionalism, behaviorism, Gestalt psychology, psychoanalysis, and humanistic psychology, each contributing to the understanding of human behavior. Modern psychology includes diverse subfields such as clinical psychology, developmental psychology, and environmental psychology, employing methods like case studies, naturalistic observation, and experimental research.