Every time we use energy, whether it's to heat our home, or fuel our car, we are converting one form of energy into another form, or into useful work. In the case of home heating, we are taking the chemical energy available in natural gas, or fuel oil, and converting that into thermal energy, or “heat,” by burning it in a furnace. Or, when we drive our car, we are using the engine to convert the chemical energy in the gasoline into mechanical work to power the wheels. These are just two examples of the “Energy Conversion Chain” which is always at work when we use energy in our homes, offices, and factories, or on the road. In each case we can visualize the complete energy conversion chain which tracks a source of “primary energy” and its conversion into the final end-use form, such as space heating or mechanical work. Whenever we use energy we should be aware of the fact that there is a complete conversion chain at work, and not just focus on the final end-use. Unfortunately, many proposals to change the ways in which we supply and use energy take only a partial view of the energy conversion chain, and do not consider the effects, or the costs, that the proposed changes would have on the complete energy supply system.