The United States remains vulnerable to terrorist and other threats posed by chemical, biological, radiological, and nuclear (CBRN) agents. Medical countermeasures such as drugs, vaccines, and diagnostic devices, can prevent or treat the effects of exposure, but few are currently available. This book examines the federal efforts needed to develop and acquire countermeasures to threats from terrorists and other sources, primarily through the Public Health Emergency Medical Countermeasures Enterprise (PHEMCE).