Overweight and obese but otherwise healthy participants (N=416) will be recruited in approximately equal numbers at two clinical centers, the University of South Carolina and the University of Vermont. Eligible participants will be randomized to one of two conditions: 1) an 18-month, 36-session group Internet behavioral weight control treatment (Internet Only) which replicates the intervention the investigators have implemented previously; or 2) the same 18-month, 36-session group Internet treatment plus financial incentives for performance of 3 key self-management behaviors (Internet+ Incentive). Both conditions will have access to the same web-based intervention platform and the same counselor-delivered intervention elements; the presence of economic incentives for behavioral and weight goals is the only difference between the conditions. Assessments will be conducted at Baseline, 2, 6, 12 and 18 months. Cost data will be collected to inform cost effectiveness evaluations.