The purpose of this section is to provide an overview about how geophysics can be used to help solve applied problems and to introduce ideas, and methodologies, that will be used throughout the gpg resource. Background to the use of geophysics, as well as a couple of examples, are provided in “Seeing Underground”. The Seven-Step procedure provides a practical framework for using geophysics. Some of the more common survey methods, and the physical properties to which they are sensitive, are presented, followed by some general descriptions about “models” and what is meant by inversion.