INTRODUCTION Modern society is built on energy technologies to provide a comfortable and safe environment@ and to produce desirable goods and services. There are many different ways to identify@ categorize and subdivide energy consuming sectors. Two examples are on the basis of end use@ such as heating@ cooling@ lighting or manufacturing@ or on the basis of the general class of activity@ such as transportation@ industrial or buildings. However@ regardless of how the energy consumption is categorized@ the efficient use of energy is desirable. Focusing on energy efficiency as a means to control energy usage@ rather than a simple reduction in energy consumption@ allows us to meet our broader economic goals without sacrificing performance desired from the activity. The link between energy efficiency and GHG emissions is clear. The principal GHG of concern is CO2@ a product of carbon-based fuels combustion. Thus@ both the efficiency of fuel burning devices and the efficiency of devices that use energy produced by other devices that burn fuel@ affect GHG emissions. Taking a broader view@ the efficiency of all the various processes in an energy conversion chain influences the total energy requirements@ and therefore the associated GHG emissions.