A convenient view of geophysical phenomena is based on the categorization of techniques according to the governing partial differential equation: the Laplace, diffusion, or wave equation. Each category is examined (nonmathematically) in the context of those borehole methods used to investigate large volumes of a rock mass away from the borehole in which the instrumentation is deployed. The published literature reflects the variety of applications, some of which occur more frequently than others. Our discussion of the physics focuses on electric-potential, electromagnetic-induction, and seismic methods, respectively, as representatives of each category. Choice of a single technique for characterization of rock masses involves a compromise which depends upon the geophysical problem and the type of information desired. The complementary nature of the information means, however, that integrated studies using two or more types of methods may be worthwhile.