From fads, crazes, and manias to collective delusions, scares, panics, and mass hysterias, history is replete with examples of remarkable social behavior. Many are fueled by fear and uncertainty; others are driven by hope and expectation. For others still, the causes are more obscure. This massive collection of extraordinary social behaviors spans more than two millennia, and attempts to place many of the episodes within their greater historical and cultural context.

Perhaps the most well-known example of unusual collective behavior occurred in 1938, when a million or more Americans were...