Publisher Summary This chapter presents a monograph discussing several methods of utilizing the data of temperature surveys in deep boreholes and the results of field, laboratory, and analytical investigations in geothermics. The objective of this monograph is a valid presentation of the state of knowledge and prediction of downhole and formations temperatures during well drilling, well completion, shut-in, and production. Potential applications of data presented in this monograph are given in several outlines—well drilling and oil/gas production, geophysics, and geology. The Society of Petroleum Engineers has suggested a set of standard symbols for use in petroleum engineering and an effort has been made to adhere to those standards. In the monograph International System (SI) of units is used with practical oilfield units in brackets. When reference data are used the original units are maintained. The coefficients in empirical equations are presented in such way that it can be used either with the practical oilfield units.