Background: One in four Veterans presenting to VA primary care suffers from mental health conditions, most commonly depression. However, due to barriers such as time constraints on providers, Veterans’ stigma about seeking mental health care, and costs associated with traveling to VA for care, most of these Veterans do not receive any treatment for their mental health problems. Mobile health (“mHealth”) is an innovative and low-cost means of expanding access to mental health care for Veterans. The effectiveness of mobile applications (apps) and other mHealth tools is emerging. Nevertheless, poor patient engagement and poor sustainability remain the Achilles’ heel of these tools. These implementation challenges greatly limit the routine use of these otherwise promising innovations. Peer Specialists (PS) can enhance patients’ engagement with apps that are intended for self-care of mental health problems by helping to orient patients to these apps and by providing technical support and accountability. Consistent with this, recent studies indicate strong support among PSs and primary care providers for using PSs to facilitate patients’ engagement with mobile apps. In combination with the recent expansion of PSs into primary care, these studies suggest that PSs may be the ideal workforce and primary care the ideal setting in which to facilitate the implementation of mHealth into routine care in VA. Significance/Impact: By capitalizing on a high-value workforce shown to improve Veterans engagement in mental health care (i.e., PSs), this research stands to accelerate the implementation of mHealth in VA, and, in turn, improve access to mental health care for Veterans. Our proposed research responds to VHA and HSR&D priorities of Access to Care, Mental Health, Population and Whole Health, and Virtual Care, as well major VA- related Legislative Priorities (MISSION Act). Innovation: PSs hold substantial promise for maximizing routine implementation of mHealth in VA, but no protocols have been designed to guide this process. In this study, we will rapidly design and then conduct a proof-of-concept test of the deployment of PSs in the implementation of mHealth in VA primary care. The protocol for PS support of mHealth will be grounded in the Whole Health model being disseminated in primary care settings VA-wide. Although we expect our PS protocol design will be easily adaptable and generalizeable to multiple apps, in this study we focus on one expert-endorsed VA app – Mood Coach. Specific Aims: (1) Conduct a formative evaluation to identify barriers and facilitators to using PSs to support implementation of mHealth in primary care. (2) Integrate the findings from the formative evaluation to design the protocol for PS’ support of mHealth in VA primary care. (3) Evaluate the feasibility, acceptability, and safety of the protocol among Veteran patients and PSs. Methodology: For Aim 1, we will hold qualitative interviews with three PSs and three primary care prov...