Exercise can significantly benefit breast cancer survivors during and after treatment. Moderate intensity aerobic exercise as well as resistance training are important. Psychological health is optimized by enjoyable exercise that develops new skills, incorporates social interaction, and occurs in a stimulating environment. Several conditions warrant exercise prescription modification (e.g., fatigue, nausea, and lymphedema). Postcancer exercise is facilitated by instilling a positive attitude, confidence, and supportive social environment. (SM)