Complex systems (e.g., infrastructure systems, economic systems, information systems) are usually exposed to various risks, including internal failures, natural disasters, and willful attacks. The risks, if not properly managed, may lead to systems unavailability, unfunctionality, and even to catastrophic events. Thus effectively accessing and managing the risks are essential to complex systems management. Hierarchical analysis (HA) is a fundamental methodology for complex systems analysis. This book for the first time discusses, compares, and integrates two branches (i.e., statistics and optimization) of HA and applied it to solve some critical problems in risk assessment and management of complex systems. The proposed methods are illustrated through case studies in various fields, including airport safety, cyber security, hurricane preparedness and etc.. The target audiences are graduate students, researchers and practitioners working in the areas of engineering, applied mathematics, applied statistics, computer science, management science, and operations research and interested in risk analysis.