Beginning in the 1980s, clinical psychologists have made significant contributions to the development, testing, and dissemination of psychological interventions for individuals undergoing stressful medical treatments or coping with chronic illness. This has been important, as there are elevated rates of mood and anxiety disorders among medical patients. Addressing the needs of patients with coronary heart disease (CHD), cancer, and cardio-pulmonary disease (COPD) is discussed. As is the case generally, cognitive behavior therapy (CBT), tailored to the specific medical illness/treatment circumstances of patients, plays a central role. More broadly, psychologists have been influential in contributing empirically based strategies to improve the health of all Americans. Effective behavior change methods for smoking cessation, dietary change, and increasing physical activity and improving fitness reduce morbidity and mortality and, of course, are key to reducing health-care costs. Thus, we urge psychological assessment and intervention as one element of standard, comprehensive, health care.