The surface of activated carbon contains a large variety of ionizable groups which lead to the sorption of either anions and/or cations from the aqueous phase. The amphoteric sorption of simple inorganic species has been described by means of the theory of surface complexation. Each kind of species is assumed to be arranged in an ordered Stern layer parallel to the surface. For the sorption of each kind of ion a set of two characteristic equilibrium parameters can be evaluated from equilibrium data. Evaluation is possible both from simple or from multicomponent systems. The parameters remain unchanged also in systems with additional ions. Evaluation of data for two commercially available carbons reveals a very satisfactory prediction of the carbon loading.