This chapter reviews S. Freud’s themes under a number of different headings, pointing to new developments in these areas, but also to some of Freud’s observations that acquire new significance in the light of these developments. Insofar as Freud was referring to the psychology of large collections of people characterised by some organised but highly emotional and irrational behaviour, he was describing hordes or mobs. The intervening years since 1921 have seen actual observations and experiments with groups of various types and sizes. The analysis of ideologies, particularly regarding their level of humanistic universalism as opposed to totalitarian sectarianism and cultism, from the viewpoint of regression in mass psychology and leadership is a new development of this approach that leaves behind the narrow Marxist application of Freud’s thinking. Re-examining Freud’s essay in the light of all these more contributions, his description of mass psychology corresponds mostly to the characteristics of large groups and mob and/or horde formation.