[en] This book is designed as an instructional manual of essential nuclear and complementary methodologies for a multidisciplinary approach to geothermal exploration development and monitoring. It provides comprehensive procedures for carrying out isotope and geochemical investigations of geothermal systems. It focuses on the three stages of geothermal studies of geothermal fluids, i.e. sampling, analysis and data interpretation. Specific chapters of the book provide some background information on the generally adopted strategy and on the behaviour of chemical and isotopic components in the geothermal environment; deal with the nature of surface thermal manifestations and sampling techniques; present analytical data handling and presentation; and concentrate on data interpretation