Nuclear security measures refer to a wide range of actions to prevent theft or diversion of nuclear material or sabotage at an installation or in transit. They could include physical protection measures, material control and accounting, personnel reliability screening, and training. A broader understanding of nuclear security also includes measures to prevent and detect illicit trafficking, cargo inspections, border security, and interdiction measures. This book examines the international effort to secure all vulnerable nuclear material around the world to prevent nuclear terrorism.