More than a century of radiation research has provided us with extensive information on health effects and biological mechanism caused by radiation exposure, especially for moderate to high dose radiation. This has contributed especially in determining the standard criteria of radiation protection. At the same time, rapid increase in radiological procedures during the past century has made significant contribution to the human health. Nowadays, medical radiation has become a major source of human exposure to ionizing radiation. Such widespread use of ionizing radiation in medical practice alerts the medical community to carefully optimize the procedures considering the benefit and risk of each patient. However, the health effects have not been confirmed for low dose and low dose-rate of radiation exposure. As medical use of radiation is expected to expand globally, the scientific research to clarify the biological effects of low-dose and low-dose-rate exposure is essential not only for optimization of the current procedures but also for future development of new technology. The aim of this workshop is to overview updated concepts of biological effects of radiation, with particular focus on medical exposure. We believe the integrative efforts of multidisciplinary fields will solve the problem, bridging the gap between radiobiology and medical use of ionizing radiation.