Overweight and inactive breast cancer survivors are at higher risk of cancer recurrence and mortality. Research suggests that losing weight and increasing activity may improve outcomes. As a result, the American Cancer Society has called for weight loss and exercise programs to be standard of care. Behaviorally based weight loss interventions have been under-utilized with breast cancer survivors and no studies have evaluated the predictors of weight loss success. Executive functions are the most common cognitive impairment in breast cancer survivors and may impact their ability to make lifestyle change. Executive functions are the top down control of behaviors and cognition and are an emerging predictor of health-related behaviors. Cancer treatment-related symptoms such as fatigue, also make behavior change a challenge. Our Primary Aim is to determine the degree to which executive functions, as measured by task performance and fMRI, account for the variance in breast cancer survivor's weight loss success. We will also determine the relationship between other cancer treatment-related symptoms, such as fatigue, and intervention success. A behavioral weight loss intervention will be provided to survivors after completing initial cancer therapy. Initial treatment (6 months) will focus on weight loss and increasing exercise. The second 6 months is a maintenance phase with reduced interaction with the interventionist. Predictors of weight loss success (executive functions, fatigue and psychological distress) will be measured at baseline, immediately post intervention (6 months), and after the 6 month maintenance phase (12 months). Executive functions will be assessed using a comprehensive battery of assessments. fMRI will be obtained concurrent with executive function testing at baseline. The impact of executive functions and other treatment-related factors on weight loss success will be determined with regression modeling to explain variability. An important step in the development of efficacious interventions is to better understand the determinants of weight loss and exercise success in overweight BC survivors. Knowledge gained from the proposed project will be used to tailor interventions for survivors that maximize weight loss and exercise.