The constantly growing demand for energy, as well as the realization during the past decade that fossil energy reserves to satisfy ever- increasing energy consumption are limited, have helped, as part of the search for alternative energy sources, to bring the subject of geothermics to its present level of significance. Practical geothermics is concerned with prospecting for and develop- ment of geothermal heat. General geothermics deals with the thermal state of our Earth as a whole. Both divisions of this field, however, contribute practical insights, and improved methods of temperature esti- mation have helped to give us a better picture of detailed thermal condi- tions. It is difficult for readers interested in this field to obtain an overview from the numerous, specialized papers that have been written on geother- mics. This book is meant to provide a thorough introduction to the subject, although the coverage is not exhaustive is detail. Geothermics is taught at universities and technical institutes, as part of the curriculum in geology. This introduction to geothermics is directed especially to students of geophysics and is meant to be used as a supple- ment to their lectures. of this work must be given to my Special thanks for the completion teacher, Prof. Dr. O. ROSENBACH. His lectures in geophysics inspired my interest in geothermics, which is still my main research area.