In this chapter, we allow static ions to move, and define a few basic transport properties: diffusion, migration, random motion of ions and solvent molecules, ambipolar diffusion of ions and counterions, and their correlation with the electrolyte viscosity and conductivity. The mathematical foundation to describe the ion movement is set: Fick’s laws, the multiple Einstein equations and the preliminary treatment of ion transport by Onsager using the Debye–Hückel model. The uniqueness of proton transport is discussed.