This chapter describes ionizing radiation and non-ionizing radiation, ways to measure it in the environment, describes the potential health effects from chronic and acute exposures as well as a discussion addressing pregnancy concerns. Background radiation from both sources are described in relation to occupational or public exposure limits and how these limits were derived. Among the subjects described are acute radiation syndrome, exposure assessment, radon, and assessment of radiation risk. Radiation protection and control measures are described and how their applications may change based on routine vs. emergency response conditions and the scale of the incident.