Abstract: This year marks one century from the first publication of Mass Psychology and the Analysis of the Ego by Sigmund Freud. What has been the importance of this text for social and political inquiry diachronically? What is its relevance today? It is to these two questions that this text is devoted. Attention is first given to the broader choreography between psychoanalysis and socio-political inquiry. Focus is then directed to the way populism research in particular has benefited from the ensuing re-orientation. Debates around ‘post-truth’ are also discussed within this context.