This chapter aims to compare Pierre Janet’s views on the dissociative responses to psychological trauma with those influenced by the psychoanalytic theory of defence mechanisms, in order to examine their accordance with some findings of contemporary psychotraumatology studies. It deals with Russell Meares’s statement that both psychoanalysis and Janet’s psychological analysis seem often compatible with clinical observations and with data from contemporary neuroscience. The chapter highlights the relevance of Janet’s ideas for contemporary psychotraumatology without implying that the psychoanalytic ones are less – or more – relevant. In the domain of contemporary psychotraumatology, the evolutionary approach to the study of motivational systems has been influential in inquiries on infant attachment disorganization as an antecedent of dissociative processes and a risk factor for posttraumatic dissociation. Freud focused on the ego functions to explain the exclusion from consciousness of drives and emotions, and the creation of the dynamic unconscious as a result of repression.