Recent dramatic increases in prevalence have made obesity the number one nutritional problem in the US. Of particular concern is the fact that, although available treatments are effective in producing clinically significant weight loss, their ability to sustain weight loss long term is poor. The present research proposal is based on a conceptual analysis of this problem that argues for greater attention to two issues related to the temporal dynamics of the challenge of long-term weight control. These are: 1) the environment is continually changing and is not supportive of weight control and 2) the intervention methods that are effective in inducing short-term changes in behaviors and weight often lose their potency over time because of habituation. A 30-month randomized trial is proposed to evaluate a maintenance-tailored treatment for obesity that is designed to address these factors. Obese men and women will be randomized to either standard behavior therapy (SBT) or to a maintenance-tailored treatment (MTT) for 18 months, followed by 12 months of no-treatment follow-up. The MTT treatment will differ from SBT because 1) it will deliberately change treatment approaches over time instead of keeping them fixed and 2) it will focus on adaptation to change as the core treatment objective. It is hypothesized that weight losses in the MTT group will be better than those in the SBT group at 30 months. It is also hypothesized that MTT participants will show better compliance to behavioral assignments, express more enjoyment and awareness of the treatment process, and have higher efficacy expectations in regard to handling future challenges to weight control.