This little book of Professor Freud’s constitutes one of the most fascinating of his contributions to the literature of psychoanalysis in recent years, and it deals with a subject of perennial interest—mass psychology. It is clearly and fascinatingly written and reasoned, stimulating to thought, and filled with brilliant suggestions. It is an admirable example of how material gained by psychoanalysis can be turned with advantage in its application to collateral regions of thought, and it is suggestive of the value of this method of procedure when such regions as the one under consideration, for example, are seen to spring into new life, to fructify, when they have been unproductive and sterilized for years. Professor Freud’s book is distinctly and decidedly a new chapter in mass psychology and in the understanding of the integrations and disintegrations of the ego.