There are now unique opportunities for research and community service for radiation experts based on a confluence of needs for reducing radiation toxicity for cancer care and preparing a medical response to a potential nuclear or radiological incident. The new opportunities include: (a) the need for agents (e.g., drugs, biologics, and natural products) to prevent and/or mitigate radiation injury; (b) the discovery and validation of biomarkers to predict radiation susceptibility and provide diagnostics for measuring dose (biodosimetry) and guiding clinical care; (c) basic research on mechanisms of radiation injury that are in common with other fields, such as inflammation, regenerative medicine, cancer, and aging; and (d) radiation biology research on mechanisms of radiation injury at the molecular, cellular, and organismal levels. The radiological/nuclear medical preparedness and response field is moving rapidly with a multipronged goal of ever-improving medical preparedness and response. This effort involves basic and translational science, device and medical countermeasure development, deployment of personnel and medical resources, access to up-to-date, just-in-time information for medical management, post-event recovery and resilience, and complex policy issues. The breadth of challenges provides an opportunity for a wide range of experts to participate. This chapter highlights the current state of the radiological/nuclear medical preparedness and response field. Given the rapidity with which research, development, and system solutions are evolving, this chapter emphasizes where to find up-to-date information.