This paper reviews the acid-base (electron donor-acceptor) interaction of 7,7,8,8-tetracyanoquinodimethane (TCNQ) with metal oxides. When TCNQ is adsorbed onto metal oxides, TCNQ anion radicals are formed as a result of electron transfer from the metal oxides to TCNQ. The measurement of the TCNQ radical concentration allows the determination of the electron donicity of single and two-component metal oxides. TCNQ adsorption is also affected significantly by the acidbase interaction between the metal oxide and solvent, the metal oxide and TCNQ, and TCNQ and the solvent. In addition, the strength and distribution of electron donor sites and enhancement of the electron donor properties of metal oxides are discussed.