This report describes and documents an ongoing analysis of the technical potential for electricity efficiency improvements in the U.S. residential sector. Previous analyses have estimated the conservation potential for other countries, states, or individual utility service territories. As concern over greenhouse gas emissions has increased, interest has grown in estimates of conservation potential for the U.S. residential sector as a whole. Earlier estimates of U.S. conservation potential are either out of date or are less detailed than is desirable for engineering-economic estimates of the costs of reducing carbon emissions. This study represents the most elaborate assessment to date of U.S. residential sector electricity efficiency improvements. It relies on regional disaggregation of input data, a stateof- the-art database of appliance efficiency and costs developed for the U.S. Department of Energy, and detailed analysis of thermal integrity measures in single-family dwellings. Fuel switching from electricity to direct use of natural gas has been included for water heaters, ranges, and clothes dryers. Advanced technologies (including "superwindows", spectrallyselective glazings, evacuated panels for refrigerators, and heat-pump water heaters) have been included based on engineering estimates of their costs and dates of availability. Some promising efficiency technologies have been omitted because we lacked data, including thermal integrity improvements for new and existing multifamily buildings and mobile homes, integrated appliances, and advanced insulation technologies for new singlefamily homes. This study also does not include load management technologies (which may improve the overall efficiency of the electric utility system) or electrotechnologies that may increase the use of electricity but reduce primary energy consumption. Efficiency improvements have been characterized in terms of their cost of conserved energy ($/kWh), for convenient comparison with the cost of competing electricity generating technologies. Figure ES-1 summarizes the results of this cost analysis. The total technical potential (without considering cost) is about 486 TWh, or about 48% of the frozen efficiency baseline. Total technical potential savings costing less than 7.6¢/kWh are 404 TWh/year by 2010, at an average cost of 3.4 ¢/kWh. If fully captured, savings costing less than 7.6¢/kWh would correspond to the output of 70-75 baseload (1000 MW) coal or nuclear plants.