Energy is the lifeblood of our economies, and its infrastructure critically affects all of our lives in virtually every activity. For every economy throughout history, one fact has held true: economic development requires energy. How we access, transfer and transform this energy into the useful work of heating, lighting and motion forms what we call an energy system, a set of interrelated elements from the capturing of natural resources to processing and refining to transportation and distribution and finally to consumption. Energy systems, however, are not simply about technology. They are multidimensional, involving natural resources, technology processes, and economic and social institutions. All of these variables interact to produce the outcome of an energy system.