This book offers a unique scientific approach to the new field of critical infrastructure protection: it uses network theory, optimization theory, and simulation software to analyze and understand how infrastructure sectors evolve, where they are vulnerable, and how they can best be protected. The author demonstrates that infrastructure sectors as diverse as water, power, energy, telecommunications, and the Internet have remarkably similar structures. This observation leads to a rigorous approach to vulnerability analysis in all of these sectors. The analyst can then decide the best way to allocate limited funds to minimize risk, regardless of industry sector.