Geothermal energy is a form of renewable energy derived from heat deep in the earth's crust. Enormous amounts of thermal energy are continuously generated by the decay of radioactive isotopes of underground rocks and stored in our globe's interior. This heat is as inexhaustible and renewable as solar energy. This heat is brought to the near-surface by thermal conduction and by intrusion into the earth's crust of molten magma originating from great depth. As groundwater is heated, geothermal energy is produced in the form of hot water and steam. The heated groundwater can be used for direct heating of homes and greenhouses, for vegetable drying, and for a number of other uses. These are known as direct uses of geothermal energy. Geothermal energy is also used for electricity production. This book presents leading-edge research in a field destined for increased attention throughout the world.