Wide in scope, this classroom-tested book is the only one to emphasize a scientific approach to protecting the key infrastructures components of a nation. It analyzes the complex network of entities that make up a nation's infrastructure, and identifies vulnerabilities and risks in various sectors by combining network science, complexity theory, risk analysis, and modeling and simulation. This approach reduces the complex problem of protecting water supplies, energy pipelines, telecommunication stations, power grid, and Internet and Web networks to a much simpler problem of protecting a few critical nodes. The new third edition of incorporates a broader selection of ideas and sectors than the previous book. Divided into three sections, the first part looks at the historical origins of homeland security and critical infrastructure, and emphasizes current policy. The second examines theory and foundations, highlighting risk and resilience in the context of complexity theory, network science, and the prevailing theories of catastrophe. The last part covers the individual sectors, including communications, internet, cyber threats, information technology, social networks, SCADA, water and water treatment, energy, and more. is an important book for upper-division undergraduates and first-year graduate students in political science, history, public administration, and computer technology. It will also be of great interest to professional security experts and policymakers.