Leon Festinger was an American social psychologist who originated the theory of cognitive dissonance and social comparison theory. The rejection of the previously dominant behaviorist view of social psychology by demonstrating the inadequacy of stimulus-response conditioning accounts of human behavior is largely attributed to his theories and research. Festinger is also credited with advancing the use of laboratory experimentation in social psychology, although he simultaneously stressed the importance of studying real-life situations, a principle he practiced when personally infiltrating a doomsday cult. He is also known in social network theory for the proximity effect.

Social psychology is the scientific study of how thoughts, feelings, and behaviors are influenced by the actual, imagined, or implied presence of others. Social psychologists typically explain human behavior as a result of the relationship between mental states and social situations, studying the social conditions under which thoughts, feelings, and behaviors occur, and how these variables influence social interactions.