Radiological and nuclear incidents are low probability but very high risk events. Measures can be, and have been, implemented to limit or prevent the impact on the public. Preparedness, however, remains the key to minimizing morbidity and mortality. Incidents may be related to hospital-based mis-administration of radiation in interventional radiology or nuclear medicine, industrial or nuclear power plant accidents. Safety and security measures are in place to prevent or mitigate such events. Despite efforts to prevent them, terrorist-perpetrated incidents with, for example, a radiological dispersal device (RDD) are also possible. Due to a misunderstanding of, or lack of, formal education regarding things in this realm, there can be considerable anxiety, even fear, about radiation-related incidents. Multiple studies evaluating healthcare provider willingness to report to work rank radiation as the hazard that will keep the largest number of workers at home. Even incidents that do not constitute a disaster can spiral out of control quite rapidly, placing considerable demands on community resources. Our communities will face these threats in the future and it is the responsibility of physicians and allied healthcare personnel to be trained and ready to care for those affected. The scope of resources needed to prepare for and respond to such incidents is indeed vast. It encompasses the coordinated effort of first responders and physicians, the preparedness of national agencies involved in responding to such events, and individual community cooperation and solidarity. This article reviews the approach to the short- and long-term effects of a radiological or nuclear incident on an affected population, with a specific focus on the medical and public health issues. It also summarizes the strengths and weaknesses of our current ability to respond effectively and makes recommendations to improve these capabilities.