Obesity, a condition characterized by excess body fat, carries significant health implications for both chronic disease and mortality. In the setting of escalating prevalence, the importance of obesity as a health problem in the United States is increasingly evident, as emphasized by the Surgeon General's "Call to Action to Prevent and Decrease Overweight and Obesity." Obesity is usually defined in terms of the body mass index (BMI, calculated by dividing kilograms of weight by meters of height squared), which is a measure of weight adjusted for height. Although numerous techniques are available for evaluating body fat, the variables for BMI are easy to measure. BMI has been shown to correlate closely with body fat content in adults and children. Adults with a BMI of 25 to 29.9 are identified as overweight and those with a BMI less than 30 as obese. These cutoffs are based on epidemiologic evidence of discernible, then substantial, increases in mortality. The prevalence of obesity is increasing. Data from the National Center for Health Statistics show that, over the past 40 years, obesity prevalence increased from 13% to 27% of the U.S. adult population; the prevalence of the less severe overweight category increased from 31% to 34%.Concurrently, a rise in prevalence of obesity has been noted in adolescent and pediatric populations. Obesity prevalence is higher in women; overweight is more common in men. Obesity is especially common in certain minority ethnic groups, including African Americans, some Hispanic populations, Native Americans, and Native Hawaiians. Obesity is a risk factor for major causes of death, including cardiovascular disease, some cancers, and diabetes. Obesity has also been linked with many sources of morbidity, including osteoarthritis, gall bladder disease, sleep apnea, and respiratory impairment. Excess weight is a risk factor for cancers of the colon, rectum, prostate, gall bladder, biliary tract, breast, cervix, endometrium, and ovary. It is associated with concerns of quality of life, including diminished mobility and social stigmatization. Risk associated with specific morbidity tends to increase more linearly with BMI than the risk associated with total mortality. This trend has been demonstrated most frequently for cardiovascular disorders, so we focus on those health outcomes in this systematic evidence review (SER). Key Questions addressed include: Key Question No. 1: Does Screening for Overweight and Obesity Affect Health Outcomes? Key Question No. 2: What is the Prevalence of Overweight and Obesity? Key Question No. 3: Is There a Reliable and Valid Screening Test? Key Question No. 4a: Do Any Interventions Lead to Sustained Weight Reduction? Counseling and Behavioral Interventions? Pharmacotherapy Interventions? Surgical Approaches? Key Question No. 4b: Do Interventions Improve Other Intermediate Health Outcomes? Key Question No. 5: Do Interventions Improve Final Health Outcomes? Key Question No. 6: What are the Harms of Screening and Treatment? Screening or Counseling and Behavioral Interventions? Medications? Surgical Approaches?