Chapter 2 pointed out the fact that energy use is responsible for about two-thirds of greenhouse gas emissions, which is a good reason to explore in depth in this chapter what drives energy use, how it is supplied, why countries value energy security, where its main uses are, and what greenhouse gas emissions it produces. The chapter then focuses on electricity production. Improving the efficiency of power plants, shifting from coal to gas, nuclear power, renewable energy, and capture and storage of CO2 from power plants can all help to reduce greenhouse gas emissions. The status of these technologies and their costs are discussed, as well as the competition between these technologies when reducing overall emissions from electricity supply. Economic, security, health, environment, and other considerations in choosing an optimal fuel mix for electricity generation are explored. Technology and economics present a fairly optimistic prospect for drastic emissions reductions. Implementing these opportunities however is hard. Selecting the right policies to provide incentives for implementation by business and individuals is crucial. On-the-ground experience is growing and lessons for effective policy choices can be drawn.