Asia has an enormous, largely untapped, opportunity to save money and cut growth in greenhouse gas emissions by taking measures to increase energy efficiency in buildings. Energy efficiency is one of the quickest, cheapest, cleanest ways to address energy and environmental challenges. In China, gaining a megawatt of electricity by building more generating capacity costs four to six times as much as saving a megawatt through greater efficiency–and that ignores the environmental costs of using fossil fuels. Yet China currently is building the equivalent of two 500-megawatt power plants every week. More than half of the world’s new construction is taking place in China and India alone. Buildings account for around 30 percent of the world’s total energy consumption and a similar percentage of the world’s greenhouse gas emissions. The way buildings are designed and constructed today not only will have an impact on their operating costs, but will affect the world’s energy consumption patterns and environmental conditions for many years to come.