he Marine Corps Operational Stress Control and Readiness (OSCAR) program embeds mental health personnel within Marine Corps units and extends their reach by training officers and noncommissioned officers to recognize Marines showing signs of stress and intervene early. RAND Corporation researchers conducted an outcome evaluation of the OSCAR program that included four components: (1) a quasi-experimental study that compared Marines in OSCAR-trained and non-OSCAR-trained battalions on a wide array of stress-related outcomes before and after deployment, (2) a longitudinal pre- and postdeployment survey of perceptions of OSCAR among Marines who attended OSCAR training, (3) focus groups with Marines, and (4) semistructured interviews with commanding officersof battalions that had received OSCAR training. Results indicated that, after the authors adjust for a wide array of baseline characteristics and deployment experiences, Marines in OSCAR-trained battalions were more likely than those in non-OSCAR-trainedbattalions to report having sought help with stress problems from a peer, leader, or corpsman - behavior that is consistent with OSCAR goals. In addition, Marines considered OSCAR a valuable tool for enhancing combat and operational stress response and recovery efforts in the Marine Corps. However, this evaluation did not find evidence that OSCAR affected the key mental health outcomes it was designed to address. Thus, the results of this evaluation do not support the continuation of OSCAR in its currentform. Based on lessons learned about OSCAR from this evaluation, other research, and best practices for program improvement and implementation, recommendations for improving combat and operational stress training in the Marine Corps are offered.