OBJECTIVES: This study evaluated theoretically derived mechanisms and common therapeutic factors to test their role in accounting for pain-related outcome change during group-delivered cognitive therapy, mindfulness meditation, and mindfulness-based cognitive therapy for chronic low back pain. METHODS: A secondary analysis of a pilot randomized controlled trial was used to explore the primary mechanisms of pretreatment to posttreatment changes in pain control beliefs, mindful observing, and pain catastrophizing, and the secondary common factor mechanisms of therapeutic alliance, group cohesion, and amount of at-home skill practice during treatment. The primary outcome was pain interference; pain intensity was a secondary outcome. RESULTS: Large effect size changes in the 3 primary mechanisms and the outcome variables were found across the conditions. Across all 3 treatment conditions, change in pain control beliefs and pain catastrophizing were significantly associated with improved pain interference, but not pain intensity. Therapeutic alliance was significantly associated with pain intensity improvement and change in the therapy-specific mechanisms across the 3 conditions. Mindful observing, group cohesion, and amount of at-home practice were not significantly associated with changes in the outcomes. DISCUSSION: Cognitive therapy, mindfulness meditation, and mindfulness-based cognitive therapy for chronic low back pain were all associated with significant changes in the primary mechanisms to a similar degree. Change in perceived pain control and pain catastrophizing emerged as potential "meta-mechanisms" that might be a shared pathway that contributes to improved pain-related outcomes across treatments. Further, strong working alliance may represent a critical therapeutic process that both promotes and interacts with therapeutic techniques to influence outcome.