Abstract Chronic low back pain (CLBP) is a significant problem affecting millions of Americans. Psychosocial approaches have been shown to be efficacious for addressing the multidimensional nature of CLBP. Three of the most widely implemented nonpharmacological techniques for CLBP management are Cognitive Therapy (CT), Mindfulness Meditation (MM), and Behavioral Activation (BA). However, there is a critical lack of research examining if these techniques work via the mechanisms specified by theory. Research examining mechanisms ? how does treatment work (mediation) ? is needed. Moreover, although past research underscores the problem of relapse following treatment, the mechanisms underlying the loss of treatment- related gains (experienced by many but not all individuals) are not well understood; hence relapse prevention interventions lack a precise, empirically guided formulation. Ecological momentary assessment (EMA) and ActiGraph technology embedded within a randomized controlled trial, consisting of daily measures of process and outcome, is ideal for testing mechanism models both during treatment and during the critical period following treatment. Thus, the current proposal seeks to utilize EMA and ActiGraph to examine if changes in cognitive content, cognitive process, and activity level are mechanisms specific to CT, MM and BA respectively for reducing pain interference (primary outcome), or if they are mechanisms shared by CT, MM and BA. Time course of lagged effects will be examined within the context of the specific and shared mechanisms model both during treatment and during the critical time epoch immediately following treatment. Elucidating the mechanisms of these three specific pain coping skills will lead to streamlined CLBP interventions, and provide a basis for development of precisely formulated relapse prevention interventions.