Psychosocial interventions are attractive options for treating chronic low back pain, and many approaches now have strong support for efficacy. However, few empirical data address whether psychosocial pain treatments work because of mechanisms specified by theory, and thus investigators know very little about HOW our treatments work. It may be that different treatments work via distinct pathways that are specific to a given treatment (single effect model), or it may be that different treatments work to the extent they all operate via key mechanisms that they share (additive effects model). Examination of specific and/or shared effects on outcomes of mechanisms will provide theoretical and empirical rationale for enhancing procedures and techniques most closely linked to strong outcomes and incorporating them into future interventions, while limiting the use of others that may be revealed as inert.

Inclusion Criteria:

• significant daily chronic pain intensity (at least 4 on a 10-point scale; see below) and interference in performing daily activities due to pain (at least 3 on a 6-point scale; see below) for at least 6 months
• musculoskeletal pain of the low back and/or leg pain that may be related to history of degenerative disk disease, spinal stenosis, or disk herniation (radiculopathy subcategory), or muscular or ligamentous strain (chronic myofascial pain subcategory)
• age between 18 and 75 years.

Exclusion Criteria:

• meet criteria for alcohol or substance abuse problems
• meet criteria for past or present psychotic or bipolar disorders
• inability to understand English well enough to complete questionnaires or to participate in therapy
• active suicidal ideation with intent
• pain is due to malignant conditions (eg, cancer, rheumatoid arthritis), migraine or tension headache, fibromyalgia or complex regional pain syndrome.