Immune parameters are relevant for assessment of prognosis and therapy response in breast cancer. A considerable heterogeneity of immune activation has been described in breast cancer, which is relevant for the development of new therapeutic strategies. Tumor-infiltrating lymphocytes (TILs), in particular stromal TILs, have been established as an important biomarker for identification of tumors with preexisting immune activation, which is associated with improved therapy response and improved prognosis, particularly in triple-negative and HER2-positive breast carcinoma. For evaluation of TILs, the standardized guidelines by Immuno-Oncology Biomarker Working Group, which were published in 2014, should be used. Extensive training material developed by the International Immuno-Oncology Biomarker Working Group is available online. The good prognosis of tumors with low tumor stage and high immune cell content shown in retrospective cohorts is the basis for the current development of de-escalation clinical trial concepts. In addition, the preexisting immunogenicity in some tumors raised the hypothesis that modulation of the immune system with immunotherapy, in particular the combination of chemotherapy and immunotherapy, could be a promising strategy. Clinical trials such as the KN-522 study show that with this strategy an improved response in the neoadjuvant situation and an improved prognosis can be achieved.