Obesity and low levels of physical activity are associated with a higher risk of breast cancer recurrence and mortality. Currently, over 65% of breast cancer survivors are overweight or obese, and fewer than 30% engage in recommended levels of physical activity. The reason for low adherence to lifestyle guidelines is likely multifactorial. Given the continuing trend of increased obesity and physical inactivity in the United States, worldwide and in breast cancer survivors, more research showing the direct effect of weight loss and/or exercise on breast cancer recurrence and mortality is needed. Many exercise interventions have examined the impact of increasing exercise on changes in quality of life, with most studies showing a favorable effect of exercise on quality of life. Smaller Phase II randomized trials using biomarkers as surrogate endpoints is likely appropriate to answer questions regarding mechanisms of action, exercise type, volume, and intensity, yet a definitive trial of weight loss and exercise on disease-free survival is critical for moving the field forward. Research is also necessary on how to disseminate lifestyle interventions into the clinic and community that lead to clinically meaningful weight losses of at least 5% that are maintained over time, and favorable sustained changes in physical activity levels. Changes in referrals, access, and reimbursement of lifestyle programs may lead to favorable changes in the prevalence of obesity and physical activity in breast cancer survivors and in turn rates of breast cancer recurrence and mortality.