A general, non-linear partial differential equation for transport of electric charge in fluid media is derived. It is based onthe flux equations for transport of univalent positive and negative ions in effective equilibrium with a very weak undissociated dissolved electrolyte by diffusion, electrical conduction, and convection in an incompressible fluid. It is applicable, therefore, primarily to low dielectric constant fluids. Although complicated, the equation may be reduced, on the one hand, to a linear equation by the approximation that the charge density in the fluid is very small and, on the other hand, to less complicated useful non-linear equations by the approximations that the ionic diffusivities are equal, or that the charge density is very large.