The assessment of trauma-related disorders (TRD) and dissociative disorders (DD) is not widely taught. Accurate assessment of dissociative symptoms can be challenging without adequate training. Clinicians who have not been trained in assessing TRD may mistakenly attribute TRD and DD symptoms to psychosis, bipolar disorder, borderline personality disorder, or malingering. As a result, TRD and DD are frequently underdiagnosed and misdiagnosed, preventing these highly symptomatic individuals from receiving appropriate treatment. This chapter provides a practical overview of the assessment of trauma-related and dissociative symptoms, including self-report measures and structured assessment tools that can complement the clinical interview; the assessment of common comorbidities; methods of distinguishing TRD and DD from diagnoses with similar presentations; and potential alternative explanations for apparently dissociative experiences. The chapter also discusses the possible challenges and pitfalls of using “general” psychological assessment instruments that have not been validated with individuals with complex trauma histories.