Background. Cardiac events are the leading cause of death among firefighters and occur while on-duty at an alarmingly high rate. Short, disrupted sleep is a major, modifiable risk factor for cardiovascular disease (CVD), and up to 40% of firefighters experience sufficiently severe sleep disruption to screen positive for sleep disorders. Cognitive behavioral therapy for insomnia (CBTi) is well-established as efficacious and effective within health care settings. However, the effectiveness of CBTi-informed sleep health coaching and sleep health promotion in workplace settings, and among firefighters specifically, is largely unknown. Theory-driven research is required to address this research-to-practice gap and also identify facilitators to and barriers of intervention implementation in this high-risk population. Goal. The primary objective of this proposal is to examine whether a scalable, CBTi-informed intervention, firefighter sleep health coaching (ffSHC), improves sleep disturbances when implemented in a real-world, high- demand work environment. Methods. This study proposes to conduct a stepped wedge cluster randomized controlled trial in order to examine the effectiveness of an evidence-based sleep health coaching intervention delivered to 400 career firefighters across 20 fire departments (Aim 1). The primary outcomes are (a) the pragmatic PROMIS Sleep Disturbances questionnaire and (b) the multidimensional sleep health index derived from actigraphy. Secondary and tertiary outcomes include: sleep related impairment, sleep continuity, blood pressure, heart rate, and long-term clinic-assessments of cholesterol, body mass index, and blood pressure. To advance implementation science, this project will employ the Integrated Promotion Action on Research Implementation in Health Services (iPARIHS) framework to guide a mixed methods formative evaluation (Aim 2a) of intervention adaptations and implementation strategies. A theory-based process evaluation (Aim 2b) is embedded within the clinical trial to explore combinations of factors that promote agency-level implementation and to inform future implementation research in public safety settings. Significance and Innovation. This research will accelerate the translation of sleep health intervention to workplace wellness and advance implementation science through the application of the iPARIHS framework. The use of sleep health coaches is innovative and models how programs may expand reach to address the global problem of insufficient sleep. The long-term goal of this research is to provide critical knowledge that facilitates the widespread implementation, dissemination, and sustained utilization of sleep health intervention to promote continuous, sufficient sleep and ultimately mitigate CVD risk. Achievement of study goals will improve the health and wellness of firefighters, a population whose health is vital to assuring public safety and supporting community resiliency.