Dissociative identity disorder (DID) is a posttraumatic psychobiological syndrome that is both an adaptive response to an inescapable and traumatizing childhood environment and a psychiatric disorder. This condition is associated with substantial financial, personal, and societal costs, but is significantly understudied in part due to historical controversy and modern-day misunderstanding. Neurobiological mechanistic understanding of DID has the capacity to aid in assessment, to reveal novel brain-based treatment modalities, and to decrease stigma. Given the importance of biological research on DID, this chapter provides an overview of the current state of the literature on neurobiological markers associated with DID. Structural abnormalities in DID span subcortical and cortical regions. Functional neuroimaging studies point toward DID-related differences in self-related thinking, implicit emotion processing, working memory, spatial memory, and at rest. Functional connectivity studies implicate altered communication between key neurocognitive networks in the brain. Future research elucidating the prognostic implications of these brain-based biomarkers of DID is warranted. Ultimately, identifying how the brain changes in DID will inform neurobiological and physiological models of stress, illuminate roles that distinct brain regions play during shifts between states of consciousness, and expand our understanding of identity.