This volume presents mathematical and physical foundations common to all EM methods. There are chapters on numerical and analog modeling. The chapters on electrical properties of rocks and resistivity characteristics of geologic targets helps envisage different kinds of ground structures that may be dealt with and the effect of various factors on observed conductivities of rocks. Basic principles of modern instrument design are in “Detection of Repetitive Electromagnetic Signals.” The last chapter discusses the principles of EM inversion as a first step toward achieving the elusive goal of automatic interpretation of EM data.