Most of the examples of collective behavior mentioned above are instances of crowd behavior. The classic treatment of crowds is Gustave LeBon, The Crowd: A Study of the Popular Mind (1896), in which LeBon shows himself to be a frightened aristocrat.

He interprets the crowd episodes of the French Revolution as irrational reversions to animal emotion, and]] such reversions as characteristic of crowds in general. Freud expresses a similar view in his Group Psychology and the Analysis of the Ego (1922).

Robert Park and Herbert Blumer see crowds as emotional, but as capable of any emotion, not only the negative ones of anger and fear.

All of these writers acknowledge that there are crowds in which the participants are not assembled in one place. Turner and Killian refer to such episodes as diffuse crowds, examples being stock market booms, panics about sexual perils, and "Red scares."