Radiation has been used to treat breast cancer since shortly after Roentgen discovered X-rays in 1895. Yet, despite playing a central role in breast cancer management for over a century, the role of breast radiotherapy continues to evolve rapidly as our understanding of breast cancer biology and risk grows. Historically, nearly all breast conservation patients received adjuvant radiation, though it is now known that certain patients face exceedingly low recurrence risk and may not benefit appreciably from radiation. Consequently, several ongoing efforts at radiotherapeutic de-escalation are described herein. Similarly, the evolution of regional nodal management in breast cancer has been driven by several factors, including the increasing use of effective systemic agents (leading to a decrease in the number of patients who require axillary lymph node dissection), the development of sentinel lymph node biopsy, and several studies codifying the benefit of regional nodal irradiation. Consequently, decisions regarding when to provide regional nodal irradiation have become more nuanced, relying heavily on both the extent of axillary nodal disease, surgical and systemic management decisions, and an array of pathologic risk factors. As a result of these advances, the contemporary role of radiation therapy in breast cancer treatment is now highly tailored to the individual patient and is profoundly multidisciplinary in nature.