This book discusses the geochemical evolution of the thermal waters and thermal gases in terms of the current volcano-tectonic setting and associated geological framework that makes the region very important to the geothermal scientific community. The book explains, in a didactic way, the possible applications, depending on local conditions and scales, and it presents new and stimulating ideas for future developments of this renewable energy source. Additionally, the book discusses the role(s) of possible physicochemical processes in deep hydrothermal systems, the volatile provenance and relative contributions of mantle and crustal components to total volatile inventories. It provides the reader with a thorough understanding of the geothermal systems of this region and identifi es the most suitable solutions for specifi c tasks and needs elsewhere in the world. It is the fi rst time that abundant information and data from this region, obtained from intensive research during the last few decades, is unveiled to the international geothermal community. Thus, an international readership, in the professional and academic sectors, as well as in key institutions that deal with geothermal energy, will benefit from the knowledge from geothermal research and experiences obtained from the Aegean Region.