Chronic pain encompasses a spectrum of clinical scenarios involving both peripheral and central pain syndromes. In this clinical summary, Richard S Polin MD discusses the progression of understanding about the pathophysiology of pain, culminating in the gait theory hypothesis. The author addresses pain from peripheral nerve injury, spinal cord injury, and brain injury and stroke and discusses the basic science behind the rationale for current management schemes and pain treatments (both pharmacological and surgical). The author concludes by summarizing the success (or lack thereof) of surgical treatment modalities for chronic pain. In this update, the author includes recent data on spinal cord stimulation for back pain.