Surface complexation models (SCMs) have been used extensively to describe the acid-base properties and adsorption behaviors of inorganic and organic cations and anions on many single-phase adsorbents. The success of SCMs results from the conformation of adsorption to mass-action and material-balance laws and the flexibility in adjustable parameters. However, the assumptions made in the derivation of the SCMs are really not justified and the SCMs are not so thoroughly grounded in fundamental chemistry. The SCMs are really the data-fitting model, rather than the chemical model. The premises of application of SCMs are the accurate identification of surface species and the low surface coverage. Though the application of the SCMs comes into vogue, the SCMs should be applied with caution.