Abstract Obesity is a serious risk factor for cardiovascular disease but few people have access to behavioral treatments. Technology-delivered weight loss programs have the potential to increase reach and early studies reveal modest impact. Less impressive outcomes have been produced by commercial weight loss mobile apps perhaps because they focus mostly on self-monitoring which in spite of being an essential component of behavioral weight loss interventions, has poor efficacy as a standalone intervention. Generating technology that can assist in a wider range of behavioral strategies, particularly in ways that reduce burden could increase the efficacy of technology-supported interventions. Our previous work has focused on developing technology- supported tools that help participants implement stimulus control and problem solving, two behavior change strategies heavily leveraged in traditional behavioral weight loss interventions. The goal of this application is to test the feasibility and acceptability of a comprehensive technology-delivered weight loss intervention that systematically assists users in implementing 3 essential behavioral weight loss strategies (self-monitoring, stimulus control, problem solving) and uses peer mentoring training to engage peers to assist each other in implementing these strategies. To minimize costs and maximize dissemination potential, we leverage both commercially available technologies (e.g., MyFitnessPal and Facebook) and our home grown technologies to accomplish this. The proposed technology-delivered program includes 1) MyFitnessPal for diet and exercise self-monitoring, 2) our Building Habits Together app, which includes two features we previously developed to assist participants in the behavioral strategies of stimulus control and problem solving, 3) Facebook to provide a platform to deliver intervention messages, provide counseling, and engage participants, and 4) brief peer mentor training to increase peer-to-peer interactions relating to behavioral strategies. Once refined and pre- piloted in a single arm trial of a 6-week version, we will evaluate the feasibility and acceptability of Building Habits Together relative to a standard technology-delivered weight loss intervention in a 6-month pilot randomized trial. Feasibility outcomes include use of the mobile app features (dietary self-monitoring, slip tracker, and problem solving), retention, engagement (problem solving, peer mentoring), acceptability, weight loss-related problem solving skills, burden, contamination, and counselor time. Results will provide preliminary data to support a randomized trial testing whether the Building Habits Together intervention improves weight loss outcomes over 1 year relative to a standard technology-delivered weight loss intervention. The result would then be a low cost, low user burden, entirely remotely-delivered behavioral weight loss intervention that could be readily adopted in a variety of settings.