We are familiar with fossil fuels as the primary energy resources, but the time has come to firmly establish energy efficiency as an important energy resource to be considered in future energy investment decisions. Energy efficiency is already being touted as the '6. Fuel' after coal, oil, natural gas, nuclear energy, and renewable energy (hydroelectric, wind, solar, geothermal, etc). Energy efficiency is also the cheapest resource: The cost of electricity obtained from energy efficiency is usually between 1 and 3 cents (U.S.) per kWh. Further, energy efficiency is local and labor intensive with significant benefits to the environment by displacing pollution. The impact and importance of energy efficiency is well-established in developed countries, but this is not yet the case in developing nations. Therefore, there is a need to raise awareness about energy efficiency, and this is best done by publicizing the successful applications and their impacts. As a striking example, if the refrigerators in the U.S. were to consume electric power at the 1974 levels, the U.S. would need about 30 000 MW of additional installed power to meet this extra demand, which is equivalent to the peak power of Turkey-a country of 70 million. This means 60 coal plants with an average rated power of 500 MW and a construction cost of about $60 billion. Also, the conservation measures that were put in place in 1970s and 1980s in the U.S. became sufficient to meet most power needs of the growing economy, and consequently, a total of 97 nuclear power plants at different stages of construction with a total capacity of 107 000 MW were cancelled. Energy efficiency continues to be recognized as a major energy resource. As detailed in its energy policy report Vision 2025, the U.S. plans to meet at least 50% of the expected future load growth by energy efficiency. The developing nations should take notice of these developments and give energy efficiency the highest priority in energy investment decisions to meet growing demand. Copyright (C) 2010 John Wiley & Sons, Ltd.