The growth in importance of geothermal energy as an alternative to other energy resources in recent years has led to the development of new geophysical, geological and geochemical exploration techniques which are particularly suited to the problem. Often, geothermal reservoirs have little or no direct expression, and indirect exploration methods must be used. Measurement of temperature and heat flow in holes drilled to shallow or moderate depth is a primary approach, but other techniques which are also finding application are large-scale electrical surveys, passive seismic surveys, analysis of magnetic data to detect the depth to Curie-point effects, and soil and water geochemical studies.