The peridural (epidural) membrane (PDM) is a sheath of connective tissue surrounding the epidural space and the dural sac, along with the exiting spinal nerves. In this chapter, we delve into the description and anatomic relevance of this membrane, beginning with an outline of historic observations. We emphasize that the PDM varies in thickness over its length but is a continuous structure. In some areas, it merges with the periosteum and posterior longitudinal ligament. The PDM is highly vascular and in close association with Batson’s plexus. We gather evidence from studies of vertebral canal development to enhance our understanding of PDM embryology, which is currently understudied. From its inception, the PDM appears to play both protective and supportive roles. New research suggests that the PDM may also play a role in maintaining the epidural space and coordinating the immune response. We highlight recent findings that the PDM contains nociceptors and may contribute to back pain for some patients. Future work may further elucidate these findings to improve clinical diagnoses and develop more effective solutions for spinal pathologies.