This book presents the fields of radiation oncology and radiation biology and projects the potential changes over the next 100 years. The first section describes the status of the medical specialty of radiation oncology and offers predictions for the evolution of the specialty over the next decades. The second section deals with the predictions of the future of radiation biology.  This more comprehensive and detailed section deals with two major categories: space travel and the medical and physiological consequences of long-term exposure to space irradiation, and the late effects of ionizing irradiation on humans who have received therapeutic radiotherapy.  Expanding use of high dose rate, small volume targeted stereotactic radiosurgery, and stereotactic ablative radiosurgery is expected to increase the numbers of long-term surviving patients. The medical, physiological, and radiobiological consequences of radiation late effect is described in detail. The current novel techniques of radiotherapy including FLASH irradiation, high LET particle irradiation, and novel strategies for a theranostics (combined radiographic diagnosis of metastatic deposits, and delivery of therapeutic radiation) are described, as well as the use of clinical radioisotopes in cancer therapy. This is an ideal guide for radiation oncologists and trainees who are particularly interested in where the field will progress over the next 100 years.