This supplementary issue of the Journal of Korean Medical Science is entitled “Radiation and Health,” which introduces systems and strategies of radiological protection, health effects of ionizing radiation, radiation problems in health communication, justification of diagnostic medical exposure, patient dose management, justification and optimization for nuclear medicine practices, issues related with cancer radiotherapy, and clinical imaging guidelines. I hope this issue will contribute to the global academic field of radiation safety and practices of radiotherapy. I appreciate Dr. Dong Ik Kim for his professional role as Guest Editor and all of the authors of articles in this issue for their scholarly contribution as specialists.