It is the position of the American Dietetic Association that successful weight management to improve overall health for adults requires a lifelong commitment to healthful lifestyle behaviors emphasizing sustainable and enjoyable eating practices and daily physical activity. Given the increasing incidence of overweight and obesity along with the escalating health care costs associated with weight-related illnesses, health care providers must discover how to effectively treat this complex condition. Food and nutrition professionals should stay current and skilled in weight management to assist clients in preventing weight gain, optimizing individual weight loss interventions, and achieving long-term weight loss maintenance. Using the American Dietetic Association's Evidence Analysis Process and Evidence Analysis Library, this position paper presents the current data and recommendations for weight management. The evidence supporting the value of portion control, eating frequency, meal replacements, and very-low-energy diets are discussed as well as physical activity, behavior therapy, pharmacotherapy, and surgery. Public policy changes to create environments that can assist all populations to achieve and sustain healthful lifestyle behaviors are also reviewed.