Individuals with serious mental illness have high rates of physical inactivity and unhealthy diet and also face challenges in managing their chronic medical conditions. These unhealthy lifestyles result from factors including medical comorbidity, poverty, and amotivation related to underlying mental health conditions. A range of behavioral strategies have been shown to be beneficial in improving diet and exercise in general populations. The most successful programs employ multiple components, personalization, longer duration, more frequent contact, and trained treatment providers. Setting small, achievable goals and understanding patients’ positive motivations for change are key tools for changing health behaviors and improving illness self-management. Partnerships with community organizations such as YMCAs can be helpful. These same principles also apply to populations with serious mental illness, although programs may need to be tailored to patients’ financial constraints and psychiatric symptoms.