This project seeks to better understand dietary lapses (instances of nonadherence to dietary goals), a major cause of poor outcomes during behavioral obesity treatment (BOT). Investigators propose to conduct multimodal real-time assessment of behavioral, psychosocial, and contextual characteristics to uncover lapse phenotypes (i.e., meaningful clusters of lapse behaviors, such as lapsing via overeating vs. lapsing via eating an off-plan food). Using wearable sensors and a smartphone-based assessment platform, this research will identify latent characteristics underlying different phenotypes of dietary lapses reported by individuals who are participating in an online BOT. This study will also evaluate how these emerging lapse phenotypes vary over time, between individuals, and within individuals. Such information will ultimately help the field understand how best to reduce lapses in future treatments (e.g., how much to personalize future interventions for lapse vs. generalizability of lapse phenotypes across individuals). Therefore, this study has three goals. First, investigators aim to establish lapse phenotypes by identifying clusters of behavioral, psychosocial, contextual and individual-level factors (e.g., sex, race) that differentiate lapse behaviors during weight loss and maintenance. Second, the investigators aim to test the association of lapse phenotypes with energy intake and weight change during weight loss and maintenance to determine which lapse phenotypes have the greatest impact on BOT outcomes (e.g. personal, environmental, and behavioral factors). Lastly, investigators aim to evaluate individual variability in the occurrence of lapse phenotypes during weight loss and maintenance to determine the generalizability of lapse phenotypes across individuals. Participants will be recruited through various methods including advertisements in local media, targeted online advertising, advertisements in medical and minority communities, and direct mailers. All participants will receive a well-established online BOT program for 12 months, with a 6-month maintenance period, for a total study participation of 18 months. In conjunction, they will complete 14-day monitoring periods (at baseline, 3 months, 6 months, 12 months, and 18 months) consisting of: 1) repeated daily smartphone surveys to assess personal, environmental, and behavioral factors, including automatic capture of geographic location; 2) wearing two wrist-based sensor devices to passively capture physical activity, sleep, and eating behaviors; and 3) completing telephone-based 24-hour dietary recalls to assess overall energy intake. Weight will be measured at all visits to the research center.