Publisher Summary Energy is no less crucial to the environmental dimensions of human well-being than to the economic ones. Energy use and environmental problems are strongly interrelated. Energy systems are critical to the economy of nations and are slow to change. At the same time, environmental issues are critical to energy planning because environmental constraints and the costs of coping with them are as important as resource scarcity or the monetary costs of energy technology. Investments in energy efficiency are the most cost-effective way to simultaneously reduce the risks of climate change, oil import interruption, and local air pollution, and to improve the productivity of the economy. Energy and economics interact directly through supply and demand, prices, and capital investments.