T his chapter addresses the knotty problem of differentiating bipolar spectrum disorders (BSDs) from what we are terming trauma spectrum disorders (TSpD) and how multimethod psychological assessment can be especially valuable for clinicians. As Phelps (2016) noted, one of three most difficult challenges in differentiating BSDs is the extensive overlap of symptoms and clinical presentation with posttraumatic stress disorder (PTSD). As we further discuss, this overlap becomes even more complex when differentiating BSDs from TSpD includes considering other trauma-based diagnoses of complex posttraumatic stress disorder (CPTSD) and dissociative disorders (DD). Further compounding this complexity is the reality that traumatized individuals may suffer from bipolar disorders and individuals with bipolar disorders may become traumatized by the consequences of their bipolar disorder. In accordance with the diathesis-stress (Monroe & Simons, 1991;Rosenthal, 1970) and kindling (Post et al., 2000) models, psychological trauma (PT), especially PT in childhood, may contribute environmental loading to the causation of expression of bipolar disorders (see Bender & Alloy, 2011;Maguire et al., 2008;Malkoff-Schwartz et al., 1998). The literature abounds with bicausality of these two disorder clusters.As noted in the Introduction to this book, bipolar disorders are increasingly viewed as existing on a spectrum. Consequences of dimensional, rather than categorical, approach suggests the importance of greater nuance and complexity in assessment, especially in determining the nonmanic or submanic expression