One of the most influential works of social psychology in history, The Crowd was highly instrumental in creating this field of study by analyzing, in detail, mass behavior.
The 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.

Although the volume focuses on crowd psychology, it is also brilliantly instructive on the effects of the generally accepted beliefs of a nation's citizenry on the processes of history. Among the topics covered here are general characteristics and mental unity of the crowd; the crowd's sentiments and morality; its ideas, reasoning power, and imagination; opinions and beliefs of crowds and the means used by leaders to persuade; classification of crowds, including criminal and electrical assemblages, as well as the functioning of criminal juries and parliamentary assemblies.