Thermodynamic Methods for the Study of Interfacial Regions in Electrochemical Systems.- The Electrode Potential.- The Double Layer in the Absence of Specific Adsorption.- Specific Adsorption of Ions.- Potentials of Zero Charge.- Electric Double Layer on Semiconductor Electrodes.- Insulator/Electolyte Interface.- The Adsorption of Organic Molecules.- The Double Layer in Colloidal Systems.