This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book examines the ways in which that concept has returned to centre-stage of public policy for national cyber emergencies. It introduces the concept of cyber civil defence at the national level and traces the evolution of US policy toward national cyberspace security over two decades since the Hart Rudman Commission, set up in 1999, brought a new interest in the questions. The book argues that civil defence easily translates into comprehensive security in contemporary European thinking—especially since cyber security, defence, and national security considerations alike all rest on broad-based societal awareness, preparedness, and participation. It discusses the policy evolution for critical infrastructure protection from the time of creation of the country’s first Computer Emergency Response Team as a private university-led initiative in 1993, making it one of the oldest.