 BackgroundRationale: Obesity and physical inactivity have reached epidemic proportions, resulting in increased rates of chronic disease, premature death, and substantial health care costs. Excess weight is even more prevalent in populations with serious mental illnesses SMI, in part due to medication-induced weight gain and social disadvantage. Since individuals with SMI often have cognitive deficits, specialized approaches are required to help people manage their weight. Researchers have found that specialized in-person interventions focused on diet and activity can help individuals with SMI manage their weight. However, these evidence-based practices have not been widely disseminated. Barriers to the use of these interventions include reluctance of individuals to participate in groups, difficulty finding transportation for frequent visits to clinics, a shortage of trained clinicians, and inadequate clinician time to provide the interventions. It is likely that these barriers can be addressed with a web-based weight intervention that is tailored for individuals with SMI. Specialized web-based approaches have been studied and found to be effective in this population, and can deliver content that is intensive and engaging with minimal requirements for clinician time. 