Book excerpt: Weapons of Mass Destruction are diverse and pose unique challenges to governments attempting to keep them out of the wrong hands and preparing to respond to an attack. This text analyzes Chemical, Biological, Radiological, and Nuclear (CBRN) weapons and terrorist groups with a known interest in them. It presents accessible information about the technical challenges posed by each type of weapon, assesses the threats, and reviews the US governmental responses. It provides structured CBRN case studies and allows for easy comparison of threats, challenges, and responses. The text combines weapons and policy information in one comprehensive and comparative resource for researchers and students interested in key issues in modern terrorism and international security.