Overweight and obesity are risk factors for postmenopausal breast cancer, and many women diagnosed with breast cancer, irrespective of menopausal status, gain weight after diagnosis. Weight management plays an important role in rehabilitation and recovery because obesity and/or weight gain may lead to poorer breast cancer prognosis, as well as prevalent comorbid conditions (eg, cardiovascular disease and diabetes), poorer surgical outcomes (eg, increased operating and recovery times, higher infection rates, and poorer healing), lymphedema, fatigue, functional decline, and poorer health and overall quality of life. Health care professionals should encourage weight management at all phases of the cancer care continuum as a means to potentially avoid adverse sequelae and late effects, as well as to improve overall health and possibly survival. Comprehensive approaches that involve dietary and behavior modification, and increased aerobic and strength training exercise have shown promise in either preventing weight gain or promoting weight loss, reducing biomarkers associated with inflammation and comorbidity, and improving lifestyle behaviors, functional status, and quality of life in this high-risk patient population. Cancer 2012;. © 2012 American Cancer Society.