An estimated 10-50% of patients develop persistent, disabling, & poorly understood symptoms after COVID-19 (PASC). For many, PASC is phenomenologically like CMI (e.g., Gulf War Illness). A meta-synthesis found patients with PASC have poor experiences with care. Patients report that, at best, clinicians want to support them but do not know how, and at worst, clinicians dismiss them as having a “mental health” disorder. Clinicians report poorly understood conditions, like PASC, are the most difficult conditions to manage. These descriptions of care for PASC are like those found in decades of research with CMI. Prior research has found as many as 60% of patients with these conditions are dissatisfied with care, which results in low uptake of evidence-based treatments and poor health outcomes. A critical gap exists in our understanding of how to improve the experience of care for patients with poorly understood conditions, like PASC. Our team is well- positioned to lead research to improve experiences with care for Veterans with PASC. We have led VA research efforts to understand and improve care for Veterans with CMI. This work has found 3 factors account for 40% of the variance in satisfaction with care for CMI. We have termed our approach, Concordant Care. The evidence-based Concordant Care approach involves engaging in processes that: 1) validate the patient's experience, 2) develop a shared understanding of the condition, and 3) create a patient-centered, whole health-oriented action plan to manage the condition. This is consistent with published expert opinion that Concordant Care underlies patients' (and clinicians') positive experiences of care for poorly understood conditions. Despite strong evidence supporting this care approach, there are no interventions to train clinicians on practices to provide Concordant Care for Veterans with poorly understood conditions. Our objective is to adapt, optimize, then test if a Concordant Care training improves VA clinicians' engagement in recommended practices to achieve Concordant Care (i.e., validate, shared understanding, action plan) for Veterans with PASC. Achieving this objective is feasible as we have already developed and piloted a CMI Concordant Care training for >300 VA clinicians, who rated it positively and reported it improved their practice. Our preliminary experiences suggests that our training is feasible, acceptable, and perceived as useful by VA clinicians and valued by VA program offices. Design: In Aim 1, we will adapt and optimize our Concordant Care training for PASC. The Concordant Care clinician training will include didactics, tele-mentoring sessions, and a clinician pocket card. Veterans who are cared for by trained clinicians will get a prompt to raise PASC concerns with their clinician. In Aim 2, we will conduct a randomized parallel cluster clinical trial to determine if Concordant Care training improves primary care clinicians' (n=60) provision of Concordant Care among Veter...