The Hot Dry Rock Geothermal Energy Development Program has focused worldwide attention on the facts that natural heat in the upper part of the earth's crust is an essentially inexhaustible energy resource which is accessible almost everywhere, and that practical means now exist to extract useful heat from the hot rock and bring it to the earth's surface for beneficial use. The Hot Dry Rock Program has successfully constructed and operated a prototype hot, dry rock energy system that produced heat at the temperatures and rates required for large-scale space heating and many other direct uses of heat. The Program is now in the final stages of constructing a larger, hotter system potentially capable of satisfying the energy requirements of a small, commercial, electrical-generating power plant. To create and understand the behavior of such system, it has been necessary to develop or support the development of a wide variety of equipment, instruments, techniques, and analyses. Much of this innovative technology has already been transferred to the private sector and to other research and development programs, and more is continuously being made available as its usefulness is demonstrated. This report describes some of these developments and indicates where this new technologymore » is being used or can be useful to industry, engineering, and science.« less