Dissociation, which in simple terms means not being psychologically present in `the here and now’ and which can take many forms, poses major challenges for clinicians because it is often unrecognized (`Many people in the mental health profession do not know what dissociation looks like or how to assess for it’; Danylchuk & Connors, 2017). This is despite research findings that dissociative disorders are prevalent in the general population, disproportionately so within clinical populations, and that `severe dissociative symptoms’ are a feature of complex trauma (Schwarz, Corrigan et al, 2017: Van der Hart, Nijenhuis & Steele, 2006). This session addresses the nature and varieties of dissociation with particular reference to its role and implications in the treatment of complex trauma.