Geothermal energy is abundant and renewable, but only a very small fraction can currently be converted commercially to electricity and heating value with today's technology. In recent years, the installed geothermal capacity worldwide has more than doubled. The increase in the use of geothermal energy is the result of a multi-disciplinary effort. Highlighted are some production engineering advances that have played a significant part in making geothermal a competitive renewable energy resource. (C) 2009 Elsevier Ltd. All rights reserved.