Type 2 diabetes (T2D) affects 26 million Americans and "prediabetes" affects 86 million more. If this epidemic is not addressed immediately, 23% of Americans will have T2D by 2030. Current lifestyle programs to prevent diabetes are complex to deliver, costly, and have limited scalability. Medications do not clearly modify the disease process and have a number of side effects. New approaches are needed that can address this epidemic on a population scale. mHealth technologies (e.g., smartphones) are deeply integrated into our lives and can target the daily lifestyle behaviors that underpin the T2D epidemic. The Veterans Health Administration (VHA) is an ideal setting to test mHealth approaches because they are at the forefront of harnessing smartphone technologies to deliver care with the advent of the "VA App Store." As the nation's largest integrated healthcare system, VHA has a central dissemination infrastructure to deliver smartphone interventions to over 5.5 million Veterans. BeWell24, an adaptive and multicomponent smartphone "app" was developed based on the unique needs and desires of US Veterans and VHA clinical teams. BeWell24 targets behaviors across the 24 hours - sleep, sedentary behavior, and more active behaviors - and preliminary data suggest reductions in fasting glucose among prediabetics of 12.3% in just 8 weeks of use. A dietary component will be added to the app to further enhance the potency of the intervention. The objective now is to test whether the delivery and integration of this app into routine clinical care settings can improve glycemic control over 9 months. A randomized controlled trial of 120 prediabetic Veterans is proposed. The first aim is to test whether BeWell24 significantly improves glycemic control (reduce fasting glucose and HbA1c) over 9 months relative to usual care. Objectively-measured changes is targeted behaviors (sleep, sedentary behavior, physical activity, and dietary intake) and other key cardiometabolic biomarkers (weight/body fat, blood pressure, lipids, insulin, and hs-CRP) will also be explored. The second and third aims are to assess factors impacting scalability of BeWell24 from patient and provider perspectives to optimize opportunities for large-scale dissemination if efficacious. Program reach/retention, app usage, treatment acceptability, program costs, and clinical integration factors will be studied. Unique features of this proposal are the rigorous cluster-randomized design; testing in a highly integrated, nationwide, clinical setting; and use of a highly sophisticated smartphone platform uniquely designed for the population and targets multiple health behaviors impacting T2D risk. The long-term goal is to establish an effective diabetes prevention program among Veterans that can be used to complement and enhance existing clinical support. If effective, this approach could be rapidly scaled to Veterans nationwide and could have broad applicability for other populations at disparate T2D risk as well as other disorders.