Security protections for critical infrastructure nodes are intended to minimize the risks resulting from an initiating event, whether it is an intentional malevolent act or a natural hazard. With an emphasis on protecting an infrastructure's ability to perform its mission or function, Critical Infrastructure System Security and Resiliency presents a practical methodology for developing an effective protection system that can either prevent undesired events or mitigate the consequences of such events. Developed at Sandia National Labs, the authors’ analytical approach and methodology enables decision-makers and security experts to perform and utilize risk assessments in a manner that extends beyond the theoretical to practical application. These protocols leverage expertise in modeling dependencies—optimizing system resiliency for effective physical protection system design and consequence mitigation. The book begins by focusing on the design of protection strategies to enhance the robustness of the infrastructure components. The authors present risk assessment tools and necessary metrics to offer guidance to decision-makers in applying sometimes limited resources to reduce risk and ensure operational resiliency. Our critical infrastructure is vast and made up of many component parts. In many cases, it may not be practical or affordable to secure every infrastructure node. For years, experts—as a part of the risk assessment process—have tried to better identify and distinguish higher from lower risks through risk segmentation. In the second section of the book, the authors present examples to distinguish between high and low risks and corresponding protection measures. In some cases, protection measures do not prevent undesired events from occurring. In others, protection of all infrastructure components is not feasible. As such, this section describes how to evaluate and design resilience in these unique scenarios to manage costs while most effectively ensuring infrastructure system protection. With insight from the authors’ decades of experience, this book provides a high-level, practical analytical framework that public and private sector owners and operators of critical infrastructure can use to better understand and evaluate infrastructure security strategies and policies. Strengthening the entire homeland security enterprise, the book presents a significant contribution to the science of critical infrastructure protection and resilience.