Obesity and physical inactivity have reached epidemic proportions, resulting in increased rates of a variety of chronic diseases, increased risk of death, and substantial health care costs. Individuals with serious mental illness are even more likely to be overweight or obese, which contributes to the high rate of co-morbid medical disease and early mortality found among this population. Specific individual and group-based psychoeducational interventions have repeatedly and consistently been shown to help adults with serious mental illness improve their weight. However, these require substantial time from mental health clinicians, and frequent visits by patients to mental health clinics. This creates challenges for patients who may need to travel to a medical center that provides these services, and who often have limited transportation options. It is likely that these barriers can be addressed with a computerized, web-based intervention focused on diet and exercise education, and tailored for veterans with serious mental illness. Web-based systems can deliver content that is intensive, engaging, and tailored to the needs and preferences of specific patients. Web-based systems can be delivered using computers at community-based outpatient Clinics or other settings in the community. The objective of this project is to develop and evaluate the effectiveness of a web-based intervention to help patients with serious mental illness lose weight.