In the past several years everyone has become considerably more aware of the problems of energy supply and demand. Although extensive resources of energy are available in principle, energy that is both cheap to extract and cheap to use—such as the oil and natural gas to which we have become accustomed—is very limited. The rising cost of all forms of energy is only one of the problems we associate with the provision and use of energy. The uncertainty of existing supplies—as illustrated by the Iranian revolution and by the accident at Three Mile Island—is another, though related, problem. A different kind of problem is in the development of new supplies (fluid fuels from coal, oil from shale, nuclear breeder reactors, for example); here, necessary steps in the development may be slow in coming or even unsuccessful.