Chronic back pain remains one of the most common and challenging public health problems in the U.S.. Although the amount of money spent on back pain treatments has increased substantially over the past decade in the U.S., the health and functional status of persons suffering from back pain has deteriorated. There is a clear need to identify safe, effective, and cost-effective treatment options for this often debilitating and expensive problem. Some of the more promising treatments for chronic back pain include "mind-body" therapies that address both psychological and somatic aspects of the pain experience. This randomized trial will compare the effectiveness and cost-effectiveness of Mindfulness-Based Stress Reduction (MBSR), a well-established but inadequately-studied CAM mind-body therapy, with usual care for persons with chronic low back pain and dysfunction. This trial will also compare MBSR with a conventional mind-body therapy, Cognitive-Behavioral Therapy (CBT), which has been found to be a modestly to moderately effective treatment for chronic back pain. Should MBSR and/or CBT prove effective in this trial, the mechanisms (mediators) of the effects of these two different mind-body therapies on pain and dysfunction will be explored. Because CBT aims to alter patients' cognitive and behavioral responses to pain, whereas MBSR focuses on direct present moment experience and not on changing the thoughts or feelings about such experience, these two therapies are hypothesized to operate by different mechanisms. A total of 342 adults aged 20 through 70 years who have moderately to severely disabling chronic back pain will be recruited and randomized in equal proportions to MBSR, CBT, and treatment as usual (usual care). Both the MBSR and CBT interventions will be provided to groups of up to 15 participants once a week for 8 weeks. The primary outcomes will be back pain-related functional limitations (Roland scale) and pain bothersomeness (rated on a 0-10 scale). Secondary outcomes include depression, anxiety, perceived stress, pain interference with activities, and sleep disturbance. Outcomes will be measured 4, 8, 26, and 52 weeks after randomization. If MBSR is at least moderately more effective than usual care, this safe and relatively inexpensive therapy would provide an appealing treatment option for chronic back pain that could be made more widely available. Because of the high prevalence and costs of chronic back pain, treatments with even modest impact on pain and function could produce a large benefit on a population level.