The following work is devoted to an account of the characteristics of crowds. The whole of the common characteristics with which heredity endows the individuals of a race constitute the genius of the race. When, however, a certain number of these individuals are gathered together in a crowd for purposes of action, observation proves that, from the mere fact of their being assembled, there result certain new psychological characteristics, which are added to the racial characteristics and differ from them at times to a very considerable degree. Organised crowds have always played an important part in the life of peoples, but this part has never been of such moment as at present. The substitution of the unconscious action of crowds for the conscious activity of individuals is one of the principal characteristics of the present age.