Charles-Marie Gustave Le Bon was a leading French polymath whose areas of interest included anthropology, psychology, sociology, medicine, invention, and physics. He is best known for his 1895 work The Crowd: A Study of the Popular Mind, which is considered one of the seminal works of crowd psychology.

Crowd psychology is a branch of social psychology that deals with the ways in which the psychology of a crowd is different from the psychology of the individual persons who are in the crowd. The field of crowd psychology enquires into the behaviors and thought processes of both the individual members of the crowd and the crowd as a collective social entity. The behavior of a crowd is much influenced by deindividuation, a person's loss of responsibility, and the person's impression of the universality of behavior, both of which conditions increase in magnitude with size of the crowd. Notable theorists in crowd psychology include Gustave Le Bon, Gabriel Tarde, and Sigmund Freud.