This book deals with the signatures left by geodynamic proceses in the temperature field of the Earths crust. First, it introduces briefly the established, indirect methods for interpreting the present termperature field and methods for reconstructing the thermal fields of the geological past. Then the spatial and temporal scales that are relevant for heat transport processes are described. This problem is discussed both theoretically and on the basis of data from the German Continental Deep Drilling Program (KTB). The climate of the last 200 years and the postglacial warming in central Europe are reconstructed on the basis of two sets of temperature data from shallow and deep boreholes. This book is written for an audience at an advanced undergraduate or graduate level with an understanding of basic physical principles. It avoids particular terminology, and special terms are introduced.