Many physical processes such as the flow of electrical current, the flow of heat or the laminar flow of groundwater obey a simple linear relationship that relates the flux of energy to a gradient in potential. The constant of proportionality can be the electrical conductance (resistance), the thermal conductivity or the hydraulic conductivity. Where there is no change in storage of electrical current, heat or groundwater the steady-state equations can be simply solved using finite-difference numerical models. Examples of these solution techniques are provided in this Chapter.