This technical memorandum is intended to provide readers with information that may be useful in understanding the purposes and context of the Department of Energys Weatherization Assistance Program (Weatherization). Weatherization has been in operation for over thirty years and is the largest single national residential energy efficiency program. Its primary purpose, established by law, is to increase the energy efficiency of dwellings owned or occupied by low-income persons, reduce their total residential energy expenditures, and improve their health and safety, especially low-income persons who are particularly vulnerable such as the elderly, the handicapped, and children. The data and statistics in this memorandum provide reasonable and transparent estimates of key low-income energy usage and housing characteristics. The companion appendices at the back of the memorandum explain the methods and sources used in developing the statistics.