Jaap van Ginneken's study explores the social and intellectual history of the emergence of crowd psychology in the late nineteenth century. Both the popular work of the French physician LeBon and his predecessors are shown to be influenced and closely connected with both the dramatic events and academic debates of their day. Although LeBon is generally attributed as having created the field of crowd psychology, this study demonstrates how he derived most of his key concepts from immediate predecessors, yet refused to acknowlege his debt to them. Van Ginneken traces the descendants and heirs of the original authors throughout Europe, using unpublished correspondence to shed light on their mutual relations. Recognizing that LeBon's work was by far the most popular, the success of his work is shown to have a decisive influence on many major political leaders of the twentieth century, ranging from Theodore Roosevelt and Charles de Gaulle to Mussolini and Hitler.