District Heating began conserving energy over a century ago when steam was first offered for sale. Suppliers delivered either steam or hot water through pipes directly to customers from a central plant. An important development in district heating was the use of exhaust energy from electrical generating plants. This practice declined in the United States when cheap fossil fuels reduced the incentive to conserve. Some large city utilities such as Consolidated Edison of New York and Detroit Edison continues selling steam mainly to commercial customers. After World War II, district heating expanded substantially in Europe. Today in the U.S., the past is catching up with the present as energy shortages and costs make district heating an important option for conservation