The complex regional pain syndromes (CRPS I and CRPS II), also known as reflex sympathetic dystrophy and causalgia, have been recognized for the past 2,500 years and believed in for the past 150, but they have yet to be understood. These syndromes can be characterized by discrete sensory, motor, and autonomic findings, but many patients with CRPS continue to suffer for years without a diagnosis. The role of the sympathetic nervous system in maintaining these syndromes and its appropriateness as a target for treatment continue to be subjects of enduring controversy. As might be expected in a group of disorders that we still have trouble naming, much less diagnosing, it has been very difficult to reach a consensus on how to treat people afflicted with the CRPS. Recent insights into how the nervous system responds to injury are beginning to explain some of the “impossible” neurological findings that are characteristic of CRPS. These research findings may soon be translated into specific therapies targeted at the processes of neural inflammation that appear to play an important role in these syndromes. Using currently available techniques of quantitative sensory testing should allow us to improve our approach to diagnosing our patients and monitoring their responses to treatment. Incorporating these diagnostic techniques into clinical studies now promises to improve the utility of clinical research in this field. Case-series studies suggest that spinal cord stimulation is a safe and effective treatment for many people with advanced CRPS who have not obtained adequate relief with other treatments.