Energy development, interpreted broadly to mean increased provision and use of energy services, is an integral part of enhanced economic development. Advanced industrialized societies use more energy per unit of economic output and far more energy per capita than poorer societies, especially those still in a preindustrial state. Energy use per unit of output does seem to decline over time in the more advanced stages of industrialization, reflecting the adoption of increasingly more efficient technologies for energy production and utilization as well as changes in the composition of economic activity (see, e.g., Nakicenovic 1996). And energy intensity in today's developing countries probably peaks sooner and at a lower level along the development path than was the case during the industrialization of the developed world. But even with trends toward greater energy efficiency and other dampening factors, total energy use and energy use per capita continue to grow in the advanced industrialized countries, and even more rapid growth can be expected in the developing countries as their incomes advance. The fact that expanded provision and use of energy services is strongly associated with economic development leaves open how important energy is as a causal factor in economic development. Development involves a number of other steps besides those associated with energy, notably including the evolution of education and labor markets, financial institutions to support capital investment, modernization of agriculture, and provision of infrastructure for water, sanitation, and communications. This is not just an academic question; energy development competes with other development opportunities in the allocation of scarce capital and in the allocation of scarce opportunities for policy and institutional reform.