1. The problem of the masses. Crowd psychology has been seen as a precise problem since the end of the 19th century. The perspectives in which it was seen were determined for some time by the works of G. Le Bon (Psychologie de foules, 1895), G. Tarde (L’opinion et la foule, 1901) and G. Sighele (La folla delinquente, 1891). These analyses were motivated less by scientific objectiveness than by emotional reactions to far-reaching social changes, such as revolutions, restlessness …