Throughout various eras of breast cancer therapy, postmastectomy radiation therapy (PMRT) has played an important role in the treatment of locally advanced breast cancer. PMRT decreases locoregional recurrence and may improve overall survival in patients with tumors over 5 cm or positive lymph nodes. As novel cancer therapies improve survival in breast cancer, the role of radiation therapy is evolving. Individualized recommendations for PMRT dependent on pathologic response after neoadjuvant systemic therapy are under investigation. This review summarizes the role of PMRT during breast cancer therapy and discusses open questions that may change the landscape of future breast cancer treatment.