In recent years, new agents have challenged tamoxifen as the standard endocrine therapy for postmenopausal breast cancer. This article reviews developments with regard to the third-generation aromatase inhibitors (AIs)--anastrozole, letrozole and exemestane--and fulvestrant, the first of a new type of estrogen receptor antagonist that, unlike tamoxifen, has no partial agonist activity. The final results of the "Arimidex", Tamoxifen, Alone or in Combination (ATAC) trial, at a median follow-up of more than five years, and recent results from switching studies with anastrozole and exemestane, strengthen the position of these AIs as adjuvant treatment for hormone receptor-positive early breast cancer. Sequencing options for the future are also discussed because non-steroidal AIs are increasingly used early in the treatment sequence.