Thermal Structure of the Earth -- History of Geothermal Energy Use -- Geothermal Energy Resources -- Applications of Geothermal Energy -- Potential Perspectives of Geothermal Energy Utilization -- Geothermal Probes -- Geothermal Well Systems -- Hydrothermal Systems, Geothermal Doublets -- Enhanced-Geothermal-Systems, Hot-Dry-Rock Systems, Deep-Heat-Mining -- Environmental Issues Related to Deep Geothermal Systems -- Drilling Techniques for Deep Wellbores -- Geophysical Methods, Exploration and Analysis -- Testing the Hydraulic Properties of the Drilled Formations -- The Chemical Composition of Deep Geothermal Waters and Its Consequences for Planning and Operating a Geothermal Power Plant.