Two common types of experimental data are analyzed: (1) ζ potential versus concentration, and (2) surface charge versus ionic strength versus pH. It is shown that these phenomena are governed by the competing phenomena: (1) adsorption of ions from solution, (2) dissociation of surface groups due to chemical surface reactions, and (3) the thickness of the electrical double layer due to counterions. In the case of adsorption, the following was found. At low concentration, the adsorption effect dominates, and the ζ potential increases in absolute value with increasing concentration. At high concentrations, the double-layer-thickness effect dominates, and the ζ potential approaches zero with increasing concentration. The ζ potential versus concentration curve can be predicted mathematically by using a multicomponent adsorption isotherm in conjunction with a relationship between the ζ potential and the surface charge. The predicted ζ potential versus concentration curves were shown to be in good agreement with experimental data in the literature for AgI sols in the presence of polyelectrolytes. For the case of surface dissociation, the following was found. For metal oxides, the surface consists of hydroxides of varying degrees of hydration. The greater the degree of hydration, the higher the pH at which the zero-point charge occurs. The surface charge can be predicted by postulating a surface reaction mechanism whose equilibrium constants depend on the surface potential. It is shown that this dependence of the equilibrium constants is the reason why the surface charge increases in absolute magnitude with increasing ionic strength. Predicted surface charge versus ionic strength versus pH curves were shown to be in good agreement with experimental data in the literature for alumina at various pH and NaCl solutions.