Jaap van Ginneken's study explores the social and intellectual history of the emergence of the field of crowd psychology in the late nineteenth century in France and Italy. Both the popular work of the French physician LeBon, considered the "father" of this field, and his predecessors are shown to be influenced and closely connected with the dramatic events and academic debates of their day. Although LeBon is generally thought of as the creator of the field of crowd psychology, this study demonstrates how he derived most of his key concepts from immediate predecessors, without acknowledging his debt to them. Professor van Ginneken traces the descendants and heirs of the original authors throughout Europe, using unpublished correspondence to shed light on their mutual relations.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 had a decisive influence on many major political leaders of the twentieth century--including Theodore Roosevelt, Charles de Gaulle, Benito Mussolini, and Adolf Hitler. The work provides an international and historiographical account of the early history of crowd psychology, emphasizing the community of better and lesser known authors in this field and placing it in the context of the major scientific debates of the day.