Nearly half of U.S. adults have or are at risk of developing type 2 diabetes. Lifestyle intervention is efficacious and the first line of prevention among adults at high risk for type 2 diabetes. Unfortunately, outcomes in real-world settings do not approach the initial efficacy trial findings, in part due to low rates of retention in the intervention. Real-world programs have particularly struggled to retain participants who identify as members of racial/ethnic groups that are disproportionately affected by type 2 diabetes, potentially exacerbating health disparities. Given the strong influence romantic partners have on one another and the shared environment, in which couples typically live, lifestyle interventions that systematically include romantic partners have the potential to address the research-practice gap. The purpose of this project is to examine the efficacy of PreventT2 Together, a couple-based lifestyle intervention our team developed. The specific aims of the research are: (1) to determine the efficacy of PreventT2 Together in a single-center, randomized clinical trial,(2) to examine baseline relationship satisfaction as a moderator and perceived partner support as a mechanism of lifestyle change, and (3) to quantify intervention retention and describe reach across recruitment methods. The investigators will recruit 162 couples (i.e., adults at high risk for type 2 diabetes and their romantic partners)from community and healthcare settings, over-sampling members of racial/ethnic minority groups. The investigators will randomize participating couples to individual (PreventT2; delivered only to partners at high risk) or couple-based (PreventT2 Together; delivered to couples) lifestyle intervention conditions. HbA1c and objectively measured moderate to vigorous physical activity (MVPA) will be collected from all participants at baseline (Pre)and at the end of the 1-year intervention (Post). Participants will also report on lifestyle factors, health outcomes, and relationship functioning at each of 13-time points (Pre, monthly, during the intervention, and post). The investigators focus on the patient-centered minimum clinically important difference (MCID) in outcomes, including objectively-measured MVPA (primary outcome), as well as other aspects of lifestyle (nutrition, sleep), health outcomes (HbA1c, weight loss, stress), and relationship functioning (perceived partner support) (secondary outcomes). Situating lifestyle intervention within the romantic relationship context in which lifestyle change occurs is likely to increase reach and improve retention and lifestyle change outcomes in real-world settings. Our community-engaged approach to the development of the intervention and design of the proposed project will ensure broad applicability and dissemination of results across communities, including racial/ethnic minority groups that have not been effectively reached and retained. CDC review and approval of PreventT2 Together for use as an alternate curriculum in the National Diabetes Prevention Program (National DPP) delivered across the U.S. underscores the scalability of the intervention. If efficacious, PreventT2 Together has the potential to impact individuals and their romantic partners' quality of life and ultimately improve real-world outcomes of lifestyle intervention to prevent type 2 diabetes.