The chapter explores the multifaceted health and wellness challenges faced by individuals living with serious mental illness (SMI), emphasizing sleep, dietary habits, physical activity, and healthcare engagement. It defines wellness behaviors as functional living skills essential for quality of life and outlines how disrupted sleep, poor diet, and sedentary lifestyles contribute to premature mortality and chronic disease. Epidemiological data reveal elevated rates of cardiometabolic, infectious, and noncommunicable diseases in this population, compounded by behavioral risk factors such as smoking, emotional eating, and physical inactivity. Etiological pathways include neurobiological, psychosocial, and environmental influences, with negative symptoms and learned helplessness impeding motivation and self-regulation. Behavioral strategies highlight the role of overt and covert reinforcement, motivational operations, and integrated care approaches. This chapter underscores the urgent need for targeted interventions that address lifestyle behaviors to improve physical and mental health outcomes in individuals with SMI.