Antigens recognized by T cells in tumors include differentiation antigens, overexpressed antigens, cancer-testis, and mutated tumor neoantigens. Ionizing radiation causes damage to multiple biomolecules by direct energy deposition or by generation of free radicals, leading to cell death when the damage cannot be repaired. Tumor cell death induced by radiation will generate specific molecular signals that are sensed by antigen-presenting cells and stimulate their maturation and ability to cross-present tumor-derived antigens to T cells. Immunogenic cell death will complement the activity of immune checkpoint inhibitors. We will provide the emerging information coming from preclinical and clinical testing about the combinations of immunotherapies and radiotherapy.