It is very rare to obtain complete 3-D information in the form of images of the microstructure of a material. Most often this information is incomplete because the resolution is inadequate, or is restricted to 2-D, via some kind of micrograph, or is not available at all. In the case of incomplete microstructural information, electrical measurements are then used to try to check a hypothesized microstructure, to see ifit can account for the measured electrical response. But even when complete microstructural information is available, if the microstructure is random, then it is not possible to analytically calculate the electrical response of the microstructure. The use of computer simulations, both to generate material shape and topology and numerically solve the electrical equations, is then required. Computer simulations allow the use of more complex hypotheses for the microstructure of a material, as the electrical response can be accurately computed for a wide range of microstructural shapes and topologies.