Geothermal resources can be considered renewable on the time-scales of technological/ societal systems and do not require the geological times of fossil fuel reserves such as coal, oil, and gas. The recovery of high-enthalpy reservoirs is accomplished at the same site from which the fluid or heat is extracted. Moreover, truly sustainable production can be achieved in doublet and heat pump systems. Generally the environmental impacts of geothermal power generation and direct use are minor, controllable, or negligible. There must be full compliance with environmental regulations, which may vary from country to country. In any case the effects must be monitored and documented (often over long periods), rated and, if necessary, reduced. (C) 2003 CNR. Published by Elsevier Ltd. All rights reserved.