Abstract: Brief mindfulness training can help veterans with posttraumatic stress disorder (PTSD) learn essential skills to manage distressing emotions and thoughts. This study sought to (a) refine the content of Primary Care Brief Mindfulness Training (PCBMT) to address PTSD symptoms and recovery, (b) improve the feasibility of training Veterans Health Administration staff to facilitate mindfulness classes, and (c) increase veteran attendance in the mindfulness classes by incorporating veteran peer specialists as PCBMT facilitators. The formative evaluation guided by the Framework for Reporting Adaptations and Modifications-Expanded included 32 mental health providers and five peer specialists who first participated in PCBMT and then provided suggestions for refinement. Qualitative responses were analyzed via rapid assessment and applied to refine PCBMT content. Next, facilitator training was delivered to providers and peers. Then, newly trained facilitators delivered PCBMT to veterans. Facilitator fidelity, veteran class attendance, satisfaction, and PTSD symptom change were assessed as adaptation outcomes. Content modifications included simplification of yoga poses, emphasis on trauma-sensitive content, and discussion of mindfulness in social situations. Training modifications included the development of a 3-day facilitator training. Context modifications incorporated role modeling and values clarification specifically for peer facilitators. Adapted PCBMT was associated with high facilitator fidelity, veteran attendance, and satisfaction and reduced PTSD symptoms (Cohen's d effect size = 0.79).