This book describes the origin and characteristics of the Earth’s thermal field, thermal flow propagation and thermal phenomena of the Earth. It describes the thermal properties of rocks and methods of thermal field measurements in boreholes, underground, at near-surface conditions which enable the principles of geothermal model development and temperature field acquisition to be understood. Processing and interpretation of geothermal data are shown on numerous field examples from different regions of the world. The book provides details on a wide variety of phenomena including; analysis of the thermal regime of permafrost, thermal waters, geysers and mud volcanoes, methods of Curie discontinuity construction and considering nonlinear effects in geothermics, as well as integration of geothermal data with other geophysical methods. This book is intended for students and researchers in the field of Earth Sciences and Environment studying thermal processes in the Earth and in the near-surface. It will be useful for specialists applying thermal field analysis in petroleum and ore geophysics and archaeological prospection.