Juvenile justice officers (JJOs)—responsible for the over 1 million youth arrested each year in the U.S.—face exceptionally high chronic workplace stress. This stress is implicated in a constellation of adverse outcomes underpinned by emotion dysregulation: depression, anxiety, and workplace burnout. Importantly, JJO workforces are comprised heavily of Black/African American and Latinx employees, and these same groups face disparities in mental health symptoms and burnout compared with peers from other racial/ethnic backgrounds. Interventions that address the effects of chronic workplace stress among JJOs thus stand to yield meaningful public health benefit while helping redress health disparities. Mindfulness-based interventions (MBIs) improve emotion regulation and reduce depression, anxiety, and burnout. JJOs express strong interest in MBIs, which can be tailored and delivered to employees during their workdays via mobile health (mHealth) technology. This project will adapt an MBI smartphone app for delivery to JJOs based on empirically-supported adaptation targets, and will conduct a feasibility clinical trial. It will build on parallel procedures and technology developed through a prior NIH award to adapt and test an MBI app for arrested youth, offering a unique, efficient, and cost-effective opportunity. The study will take place in Chicago Cook County, the 2nd largest juvenile justice system in the U.S., where the study team has conducted NIH-funded research for 18 years. To guide adaptation and implementation of the app, the team will conduct key informant interviews rooted in a theoretically-driven implementation science framework. Interviews will be held on both the individual (JJO) and organizational (leadership) levels. The team will work with professional programmers to translate the interview findings into a secure app adapted from existing source code. For the feasibility clinical trial, JJOs (n=50) will be individually randomized to use the adapted MBI app or an equally intensive control app daily for 30 days. In-app analytics will capture objective use of each app feature. An adaptive intervention design will be employed to engage non-users of both apps, whereby analytics data indicating non-use will trigger delivery of an enhanced engagement strategy (e.g., text messages encouraging use). Mental health symptoms and burnout among JJOs will be assessed at baseline, 1, and 6 months via self-report. JJOs will also complete 1-week “bursts” of ecological momentary assessment (EMA) of their objective contexts and affective states at baseline and 1 month in order to capture the mechanistic target (i.e., emotion dysregulation) in the workplace. At 1 month, both JJOs and leadership will report on acceptability and feasibility via an in-depth, mixed-methods design. Completion of this study will develop building blocks for high-impact, large-scale trials that formally evaluate the adapted MBI app. The use of theoretically- driven implementa...