Infrastructure reliability, in its most general sense, refers to whether a system performs as expected. Reliability is relative, depending on the perspective of the infrastructure user. Safety and security are key components for the concept of reliability, since they pertain to basic survival, and are prerequisites for others. Safety and security are defined, and their emergence as core concepts in infrastructure reliability is described. Infrastructure security now relates to a set of critical infrastructures. Factors that potentially compromise infrastructure security include how infrastructure is spatially distributed and interrelated or interdependent with other infrastructures. Risk-based analytical approaches, and alternatives to these approaches, have arisen to address the likelihood and form of attacks as well as the consequences of attacks on infrastructure. Selected examples of these methodologies are presented. Resource allocation at the federal level emphasizes a risk-based approach, though the nature of risks faced by critical infrastructures, how these risks should be quantified, what analytical tools should be used to produce such estimates, at what geographic scale, and how they are to be incorporated into prioritization schemes are still a subject of considerable debate.