Intraoperative radiotherapy (IORT), as a method in the subspecialty of interventional radiation oncology, is one of the most dynamically growing fields in oncology. During the last decade, the number of centers offering IORT to patients has rapidly increased. There are more than 300 active IORT centers worldwide. This interest has mainly been stimulated by the clinical benefits of IORT in breast cancer. The 2nd edition of this handbook includes the basics of the IORT principles, a detailed description of techniques for IORT and a review of ongoing trials showing the benefits of this method in the treatment of breast cancer.