Our nation?s security as well as the quality of life of its citizenry depends on the continuous reliable operation of a collection of complicated interdependent infrastructures including transportation, electric power, oil, gas, telecommunications and emergency services. A disruption in one infrastructure can quickly and significantly impact another, causing ripples across the nation. Our infrastructures are increasingly reliant on new information technologies and the Internet to operate, often being connected to one another via electronic, informational links. While these technologies allow for enormous gains in efficiency, they also create new vulnerabilities. The focus of this paper is the development of a unifying mathematical framework to represent these "mega infrastructures" and a collection of algorithms that can be used to estimate performance and optimize investment. We include a small computational example that focuses on the delivery of gas and electric services, including the underlying SCADA system that supports the gas network, to illustrate the operation of the algorithms.