PROJECT SUMMARY: Chronic pain is common, costly, and debilitating. Opioid prescription in the treatment of chronic pain is frequent and carries a consequent risk of poor treatment outcome, as well as higher morbidity and mortality in a clinically significant number of patients, particularly those who meet criteria for opioid dependence. Despite the alarming increases in prescription opiate misuse and opioid use disorder (OUD) nationally in the United States, there are few treatment options available that target both pain-related interference and OUD among patients with chronic pain. In military veterans, this issue is of particular importance as numerous reports indicate frequent use of opioids in the treatment of chronic pain, as well as increasing opioid-related problems. To date, there are no evidenced-based treatment options which aim to both reduce pain interference simultaneously addressing problematic opioid use. The overall aim of the parent study (UH3DA051241) is to determine the efficacy of an integrated psychosocial treatment in veterans with chronic pain, who are taking buprenorphine for the treatment of OUD. To examine this aim, we are utilizing a multisite randomized clinical trial design to assess the efficacy of two empirically supported interventions: Acceptance and Commitment Therapy for chronic pain and Mindfulness Based Relapse Prevention for substance use and misuse. Efficacy will be assessed by examining pain interference and opioid misuse outcomes after three months of active treatment, as well as at 6 and 12 month follow-ups. Secondary outcomes, including depression, pain-related fears, and other substance use, will also be assessed at these same follow-ups. The study will also examine the relation between within- treatment changes in treatment mechanisms, including pain acceptance, engagement in values based action, and opioid craving, and changes at post- treatment and follow-up. The results of this study will directly inform treatment of patients with chronic pain and represents a significant advance in the growing and understudied problem of OUD among patients with chronic pain. In addition to addressing the question of whether the treatment is feasible, it will further examine issues of treatment mechanisms to better inform the provision of treatment. This supplement to the parent award will support finalizing recruitment, treatment, and follow-up of the sample at three Veterans Administration Healthcare System sites, and will aid in dissemination efforts.