Geothermal energy is rapidly becoming recognized, both in the United States and abroad, as a viable source of energy which can supplement fossil fuels for electric power generation. Exploration and development of geothermal reservoirs is intensifying in the western United States and Mexico, and will continue to expand as petroleum supplies diminish and costs increase. Although geothermal energy is commonly perceived as a new and exotic energy source, it is neither. Steam has been used for electric power generation since 1904 in Larderello, Italy, and geothermal waters have been used for space heating and agricultural purposes in other parts of the world since 1890. Geothermal power generation began in the United States in 1960 at the Geysers, California, and new fields are under development in the Salton trough of southern California. Herein we will attempt to answer some of the basic questions about geothermal energy: what it is, how deposits are formed, and where these deposits are located. Special emphasis is placed on the potential geothermal resources of the Texas Gulf Coast and Trans-Pecos Texas. This discussion should provide the reader with an appreciation for both the problems and advantages of this unfamiliar form of energy as well as the potential it holds for supplying Texas with a portion of its future energy needs.