Hot dry rock (HDR) is defined as that part of a geothermal anomaly where the fluids needed for production of steam or hot water are lacking. Most of the world's geothermal resource is not present in the form of natural hydrothermal systems but as HDR. Development of this resource through the use of manmade geothermal systems is in progress in several countries. The largest of these experiments, the Fenton Hill HDR geothermal project, is funded by the U.S. Department of Energy and the governments of West Germany and Japan. This project is located a short distance west of the rim of the Valles Caldera in the Jemez Mountains of New Mexico. As the Fenton Hill experiments progressed, it became evident that the location and extent of the HDR geothermal resource in other areas should be evaluated and that potential HDR drilling sites be located as part of a comprehensive program needed to encourage its development. Because the HDR resource lacks the sharp physical and chemical contrasts produced by natural fluids, it presents different exploration problems from those of conventional hydrothermal exploration. The purpose of a workshop, held in Los Alamos, New Mexico, June 21–23, 1982, was to review geological, geochemical, and geophysical exploration methods currently used for HDR recognition and resource evaluation and to evaluate new ideas for HDR exploration.