Background: VHA primary care Veterans often have psychological distress that impairs their functioning, physical health and increases risk for suicide. This distress often goes untreated or undertreated. Innovative interventions must align with patient preferences for the content (e.g., skill-based, transdiagnostic}, format (e.g., peer support} and location of services. Primary Care Brief Mindfulness Training (PCBMT) is a series of 4 classes that teach mindfulness exercises to manage psychological distress that is consistent with treatment preferences. PCBMT has been shown to be effective in reducing psychological distress in two preliminary studies. Significance: Results from this proposed trial could lead to more engagement in evidencebased care, better Veteran health, and higher quality and more efficient VHA mental health care. The proposal fits with HSR&D priorities (mental health, Whole Health) and ORD-wide priorities to expand access to high-quality clinical trials, increase the real-world impact of research and promote inclusion and equity. Innovation and Impact: PCBMT is innovative via its delivery in primary care, use of a novel staffing strategy (peers and WH partners) and it is a transdiagnostic approach. The methods of this study are also innovative: 1) thls pragmatic clinical trial will maximize generalizability, 2) we will test components of the novel Transtherapeutic Mindfulness Framework to help the scientific community understand how mindfulness interventions impact psychological outcomes, 3) we will explore how social determinants of health (SDoH) impact care, and 4) we will integrate implementation science methods to guide future implementation efforts. Specific aims: 1. Compare PCBMT to a transdiagnostic problem solving group (Moving Forward, MF). We hypothesize that Veterans randomized to PCB MT will experience larger improvements in psychological distress (DASS-21) than MF participants. 2. Test mediators and moderators of treatment gain in PCBMT and MF. a. We hypothesize changes in transdiagnostic processes (e.g., psychological flexibility, thought suppression) will mediate the relationship between mindfulness and psychological distress. b. We will explore if SDoH (race, sex, ability to obtain necessities to live, safe housing) moderate initiation, completion and clinical benefits of PCBMT and MF. 3. Assess implementation barriers and facilitators to inform future implementation efforts. PCBMT facilitators and PACT and Whole Health administration will be interviewed following the RCT to understand factors that served as barriers and facilitators to PCBMT implementation. Methodology: The proposed study seeks to further test the effectiveness of PCBMT in three VHA primary care settings that serve diverse Veteran populations and begin to understand important implementation factors with a Hybrid Type l randomized controlled trial in primary care patients with psychological distress. Next Steps/ Implementation: Should our result...