Traumatic brain injury (TBI) is the signature wound of Veterans returning from Operations Iraqi Freedom, Operation Enduring Freedom and Operation New Dawn (OIF/OEF/OND), with up to 20 percent exposed to a mild TBI (mTBI) and experiencing persistent post-concussive symptoms. Among those with a mTBI diagnosis, the majority also suffers from stress-based psychopathology (e.g., depression, post-traumatic stress disorder, generalized anxiety disorder), as well as chronic pain. To cope with distress, pain, and other difficulties, Veterans often turn to maladaptive avoidant coping strategies which offer short term relief but exacerbate/maintain mental health problems and have detrimental long-term effects on social, occupational, and community reintegration. Unfortunately, Veterans face significant barriers to engaging in mental health treatment, including stigma, the belief that one should overcome psychological difficulties on his/her own, and concern that receiving such care would negatively impact their careers. Practical barriers, including time constraints, distance from a treatment facility, and competing priorities (e.g., work and family demands), are also barriers to care. Even among Veterans who start mental health treatment, only a small minority complete a recommended course of evidence-based therapy. Acceptance and Commitment Therapy (ACT) is a trans-diagnostic treatment model that helps patients to overcome avoidance by promoting acceptance-based coping and engagement in meaningful life activities. In this context, Veterans are asked to think about their ?new mission(s)? after leaving the military and the importance of engaging in actions that fulfill their mission even when it may be difficult. ACT has established efficacy in the treatment of depression, anxiety, and chronic pain, and has been effectively implemented in various treatment-delivery formats, including 1-day group workshops. A 1-day ACT workshop addresses specific needs of Veterans with mTBI, stress-based psychopathology, and chronic pain (polytrauma triad) and important barriers to treatment. It 1) is trans-diagnostic (i.e., applies to more than one condition); 2) targets avoidance-based coping; 3) cultivates acceptance-based coping and builds on Veteran?s values and goals to motivate them to make difficult decisions; 4) is delivered efficiently and thus more accessible; 5) is less stigmatizing and thus acceptable; and 6) address problems with treatment adherence and completion. With the support of an RR&D SPiRE pilot grant, the PIs developed a 1-day ?ACT on Life? workshop tailored specifically for the needs of Veterans with mTBI, stress-based psychopathology, and chronic pain. Veterans with this polytrauma were then randomly assigned to the ?ACT on Life? workshop (N=20) or to Treatment as Usual (TAU; N=12). All Veterans attending the 1-day ACT workshop completed it, and relative to TAU, exhibited greater improvements in distress and reintegration at the 3-month follow-up (effect sizes .68 and .47, respectively). Building on these promising preliminary findings, we now propose to conduct a more rigorous randomized controlled trial with 212 Veterans to compare the efficacy of the 1-day ACT workshop to an active treatment comparison (Education, Resources, and Support; ERS) on symptoms of distress and social, occupational, and community reintegration. We will also examine mediators and moderators of treatment response to identify which ACT components are directly responsible for treatment effectiveness and whether treatment benefits are constrained by various personal factors. Establishing the efficacy of a 1-day ACT workshop for OEF/OEF/OND Veterans with mTBI and multiple coexistent conditions addresses key priorities of VHA RR&D: 1. developing interventions which will improve the psychological health status of Veterans who have specific needs; and 2. enhancing the community, social, and occupational reintegration and functioning of post-deployment Veterans so that they may function more fully in society.