Radiation therapy (RT) remains an integral component of modern breast cancer treatment paradigms. While RT is utilized primarily for its localized antitumor effects, preclinical and early clinical evidence indicate that RT generates notable changes to the tumor microenvironment (TME) that may promote systemic antitumor responses. Immunotherapy, and specifically immune checkpoint blockade (ICB), has provided a novel opportunity to enhance both local and systemic immune responses to RT in a variety of solid tumors, including breast cancer. Combinations of RT and ICB have demonstrated synergistic activity in clinical trials across multiple tumor types including non-small cell lung cancer, gastroesophageal cancer, and cervical cancer. Recent clinical successes for ICB in breast cancer in the neoadjuvant and metastatic settings provide compelling evidence for adding RT to immunotherapy in breast cancer. Indeed, RT and ICB combinations have demonstrated clinical activity and tolerable safety profiles across multiple early trials in metastatic breast cancer. This has led to several ongoing clinical trials of RT and ICB combinations in early-stage breast cancer and in the adjuvant setting. Several critical questions remain including the identification of predictive biomarkers for response, the sequencing of RT and ICB, and how to incorporate novel immune modulators that can augment response to treatment.