The U.S. population is now healthier and more long-lived than ever, and the average life expectancy for a woman born today is about 80 years. An elderly woman's life expectancy, which is related to comorbidity and functional status, is particularly important when determining the appropriate choice of adjuvant chemotherapy and endocrine therapy. In addition, the disease stage and the tumor's biologic characteristics (grade and hormone/human epidermal growth factor [HER]-2 receptor status) must be considered when formulating a treatment plan for 3 clinically distinctive breast cancer subgroups: (1) hormone receptor negative (HR−) and HER-2 negative (“triple-negative” tumors, about 15% of older patients); (2) hormone receptor positive (HR+) and HER-2 negative (the largest group comprising about 70% of older patients); and (3) HER-2 positive irrespective of HR status (about 15% of older patients). The functional status of an older woman can be estimated by a Comprehensive Geriatric Assessment (CGA). A traditional CGA is time consuming, but testing of shorter, validated CGA instruments is ongoing. Monitoring toxicity in the elderly is especially important because even low-grade toxicity can have a significant effect on function. Eligible older women should be considered for state-of-the-art treatment, including clinical trials to determine the optimal adjuvant regimens for this patient population and how the therapies affect the woman's functioning and quality of life.