ABSTRACT In 2018, an estimated 88 million Americans 18 years of age and older or approximately one-third of the adult U.S. population had prediabetes. In 2002, the Diabetes Prevention Program clinical trial demonstrated that an intensive lifestyle intervention designed to produce and maintain a 7% reduction in initial body weight and increase moderate physical activity to 150 minutes per week reduced the incidence of diabetes by 58% over 2.8 years. In 2010, Congress authorized the Centers for Disease Control and Prevention (CDC) to establish, manage, and expand the National Diabetes Prevention Program (DPP). Eligibility criteria for enrollment in the DPP (fasting glucose 100-125 mg/dl or 2-hour glucose 140-199 mg/dl or hemoglobin A1c 5.7-6.7% or high risk score on ADA/CDC prediabetes risk screener or personal history of gestational diabetes) were broader than those used in the clinical trial, the format of the intervention (group versus individual), the personnel delivering the intervention (medical personnel versus trained lay leaders), the delivery mode (in-person versus virtual (telehealth) versus online), and the duration (3 years versus 1 year) all differed from the clinical trial. Although the trial demonstrated that the intervention was both effective and cost-effective, the long-term effectiveness and cost-effectiveness of DPP-like programs implemented in real-world settings have not been established. The purpose of this proposal is to assess individual and system-level barriers to and facilitators of participation in the National DPP/Medicare DPP and to evaluate the long-term effectiveness and cost-effectiveness of the DPP as implemented in real-world settings. By assessing individual and system level barriers to and facilitators of participation in the DPP, and by evaluating the long-term effectiveness and cost-effectiveness of the DPP as implemented in real-world settings, this study will provide information critical to improving the uptake and impact of the DPP on diabetes in the United States.