The aim of the present Bachelor thesis is to give a closer look at the intraoperative radiotherapy (IORT) of breast cancer. The female breast and breast carcinoma are briefly described for their general understanding in their anatomy and histology. The standardized radiooncological treatment methods are presented on the basis of research in specialist books and studies. The interdisciplinary S3 guideline is also used for the diagnosis, treatment and aftercare of breast cancer. The main part of the work deals with the irradiation forms of the IORT. These can be carried out by means of high-energy electron radiation or low-energy photon radiation. To this end, the devices used for this purpose are also described and compared in more detail. Furthermore, the various application forms of the IORT are presented. Studies show the advantages and disadvantages of the IORT compared to a conventional whole-breast irradiation. The importance of a single IORT in comparison to percutaneous radiotherapy after a brimming operation is also shown in the latter chapters.