Since the initial studies of adjuvant therapy in the 1970s, it has become increasingly clear that chemotherapy and hormone therapy have had a substantial effect on the survival of women with early breast cancer. It was originally assumed that only women with high-risk features would derive benefit from adjuvant therapy, but it is now apparent from numerous studies that adjuvant therapy improves survival in all subgroups of women with invasive breast cancer, although the absolute benefit varies depending on tumor stage and other prognostic features. Considerable progress has been made in elucidating effective adjuvant therapy regimens, but there continue to be many unanswered questions that are being addressed in ongoing clinical trials of adjuvant hormone therapy and chemotherapy. This paper reviews the current paradigms in adjuvant therapy, the published data that have affected current practice patterns, and the current controversies.