Objectives. We sought to better understand the challenges of communicating with the public about emerging health threats, particularly threats involving toxic chemicals, biological agents, and radioactive materials. Methods. At the request of the Centers for Disease Control and Prevention, we formed an interdisciplinary consortium of investigative teams from 4 schools of public health. Over 2 years, the investigative teams conducted 79 focus group interviews with 884 participants and individual cognitive response interviews with 129 respondents, for a total sample of 1013 individuals. The investigative teams systematically compared their results with other published research in public health, risk communication, and emergency preparedness. Results. We found limited public understanding of emerging biological, chemical, and radioactive materials threats and of the differences between them; demand for concrete, accurate, and consistent information about actions needed for protection of self and family; active information seeking from media, local authorities, and selected national sources; and areas in which current emergency messaging can be improved. Conclusions. The public will respond to a threat situation by seeking protective information and taking self-protective action, underlining the critical role of effective communication in public health emergencies.