The infrastructure of the United States-the foundations on which the nation is built-is a complex system of interrelated elements. Those elements-transportation, electric power, financial institutions, communications systems, and oil and gas supply-reach into every aspect of society. Some are so critical that if they were incapacitated or destroyed, an entire region, if not the nation itself, could be debilitated. Continued operation of these systems is vital to the security and well-being of the country.