Current theories about the aetiology of nightmares and mechanisms of action that account for their successful treatment have not yet taken the polyvagal theory (Porges, 2011) into consideration. While the polyvagal theory's updated and multifaceted view of the autonomic nervous system's (ANS) response to threat has begun to transform the field of trauma treatment, most of these ideas have not yet been applied to nightmares and their treatment. This article outlines how the theory may provide a missing link in understanding specific ways that trauma and adversity lead to chronic nightmares, and it offers a way to make sense of the heterogeneity of trauma-related symptoms and concomitant responses to nightmare treatments. A review of the literature demonstrates evidence of links between measures of ANS and physiological responses to nightmares. Content similarities between threat responses described by polyvagal theory and common nightmare themes provides an additional avenue for assessment and intervention. Theories of nightmare aetiology and treatment are evaluated with respect to polyvagal theory, and lastly, a proposed treatment protocol, nightmare relief, offers a polyvagalinformed, process-experiential approach to treating nightmares, with links to clinical examples.