Reference to `parts’ of the personality is common in the psychotherapeutic literature and the term is widely used by clients and therapists alike. What we call `self’ is not unitary and mental life is subject to state fluctuation and change. To this extent `we all have parts’ (van der Kolk, 2015) and `[w]e are all multiple to some degree’ (Putnam, 2016). The language of `parts’, `ego states’, and `self-states’ is also helpful and non-stigmatising with respect to the problematic divisions of personality generated by trauma, disrupted attachment, and experiences of overwhelm, in which self-states are unintegrated and flexibility, continuity, and coherence are impeded. This session presents an introduction to `working with parts’ with particular reference to the crucial distinctions between standard ego-states which characterise health, and dissociated self-states which pertain to the impacts of complex trauma (and which `can range from very simple to extremely complex divisions of the personality’; van der Hart et al, 2006) Note that while reference to structural dissociation generated by severe early life trauma is included, this seminar does not equip participants to work with Dissociative Identity Disorder (DID).