Inclusion Criteria:  Individuals must be of overweight or obese BMI (27-50 kg/m2) Individuals must be adults (aged 18-70) Able to engage in physical activity (defined as walking two city blocks without stopping) Access and willingness to use a smartphone and internet Has one adult friend or family member who indicates willingness to serve in a support role Satisfactory completion of all enrollment procedures English Speaking  Exclusion Criteria:  Medical or psychiatric condition (e.g., cancer, type I diabetes, psychosis, full-threshold eating disorder) that may pose a risk to the participant during intervention or cause a change in weight, or limit ability to comply with the program or participate appropriately in group-based treatment Currently pregnant or breastfeeding, or planning to become pregnant in the next 24 months Use of insulin or a medication that can cause significant change in weight History of bariatric surgery Weight loss of > 5% in the previous 3 months