Modern infrastructures such as energy, transport or information and communication technologies are complex and highly interdependent systems. Modern society and economy place growing expectations and reliance on them. Failures in infrastructure systems can affect large parts of the everyday life and in inflict significant losses.

This thesis is concerned with reasoning about the dependability of national infrastructures. It takes a holistic view of national infrastructure systems and treats them as an interconnected system-of-systems. The thesis focuses on describing and analysing failure in such systems-of-systems, especially how it propagates between systems via infrastructure interdependencies.

The aim is to improve the ability to reason about interdependent infrastructure systems by reviewing notions and techniques from dependable computing and assessing how they can be applied to national infrastructure systems analysis. The thesis proposes a framework to describe and reason about complex infrastructure systems. The framework employs fault-error-failure concepts; emphasises the roles of assumptions, boundaries and structure in systems description; uses top-down system view supplemented with formal techniques. The framework is extended to include the planning process and humans as systems within the same analysis umbrella.