The Hot Dry Rock geothermal energy project began in the early 1970’s with the objective of developing a technology to make economically available the large ubiquitous thermal energy of the upper earth crust. The program has been funded by the Department of Energy (and its predecessors) and for a few years with participation by West Germany and Japan. An energy reservoir was accessed by drilling and hydraulically fracturing in the Precambrian basement rock outside the Valles Caldera of north-central New Mexico. Water was circulated through the reservoir (Phase I, 1978-1980) producing up to 5 MWt at 132ºC. A second (Phase II) reservoir has been established with a deeper pair of holes and an initial flow test completed producing about 10 MWt at 190ºC. These accomplishments have been supported and paralleled by developments in drilling, well completion and instrumentation hardware. Acoustic or microseismic fracture mapping and geochemistry studies in addition to hydraulic and thermal data contribute to reservoir analyses. Studies of some of the estimated 430,000 quads of HDR resources in the United States have been made with special attention focused on sites most advantageous for early development. 3 figs., 1 tab., 12 refs.