The evolution of thinking about energy is discussed. When the authors began collaborating 20 years ago, energy was typically considered from a growth-oriented, supply-side perspective, with a focus on consumption trends and how to expand supplies to meet rising demand. They were deeply troubled by the environmental, security and equity implications of that approach. For instance, about two billion people lack access to affordable modern energy, seriously limiting their opportunities for a better life. And energy is a significant contributor to environmental problems, including indoor air pollution, urban air pollution, acidification, and global warming. The authors saw the need toevolve a different perspective in which energy is provided in ways that help solve such serious problems. They argued that energy must become an instrument for advancing sustainable development--economically viable, need-oriented, self-reliant and environmentally sound development--and that the focus should be on the end uses of energy and the services that energy provides. Energy technological options that can help meet sustainable development goals are discussed. The necessity of developing and employing innovative technological solutions is stressed. The possibilities of technological leapfrogging that could enable developing countries to avoid repeating the mistakes of the industrialized countries is illustrated with a discussion of ethanol in Brazil. The role foreign direct investment might play in bringing advanced technologies to developing countries is highlighted. Near- and long-term strategies for rural energy are discussed. Finally, policy issues are considered for evolving the energy system so that it will be consistent with and supportive of sustainable development. [ABSTRACT FROM AUTHOR]