With the threat of future radiological or nuclear events, there is a need to model and develop new medical countermeasures for managing large-scale population exposures to radiation. The field of radiation biodosimetry has advanced far beyond its original objectives to identify new methodologies to quantitate unknown levels of radiation exposure that may be applied in a mass screening setting. New research in the areas of genomics, proteomics, metabolomics, transcriptomics, and electron paramagnetic resonance (EPR) applications have identified novel biological indicators of radiation injury from a diverse array of biological sample materials, and studies continue to develop more advanced models of radiation exposure and injury. In this article, we identify the urgent need for new biodosimetry assessment technologies, describe how biodosimetry diagnostics work in the context of a broad range of radiation exposure types and scenarios, review the current state of the science, and assess how well integrated biodosimetry resources are in the national radiological emergency response framework.