This book provides a comprehensive introduction to the chemistry of geothermal water and gas discharges, including the application of isotope studies, and assumes no prior knowledge of geothermal fluid chemistry. The critical interpretation of discharge chemistry in terms of resource evaluation and the development of hydrological models are emphasized. The text is divided into two parts: following an introduction to the genesis of geothermal fluids, the first part deals with water, gas and isotope chemistry. The chemical behaviour of common constituents and the interpretation of the chemical signature of the fluids are discussed, with stress placed on the evaluation of reservoir conditions and subsurface flow regimes. The second part describes techniques in geochemical exploration for geothermal resources. Individual chapters deal with the planning, execution and critical evaluation of water, gas and soil surveys. Analytical methods, units and data presentation techniques are also covered in this section. Both students and experienced geothermal scientists will find this book of value both as an introductory text to the application of geothermal chemistry, and as a reference handbook to geochemical techniques. Part Two will also be of interest to exploration and environmental geochemists in general, as the survey techniques detailed have applications beyond geothermal resource evaluation.