Classical thermodynamics is used in combination with the electrostatic theory to develop generalized expressions for the electrochemical potentials of neutral and ionic species of multicomponent layers adsorbed on electrode surfaces. The proposed approach allows all kinds of dipole-dipole, field-dipole, ion-field and ion-image interactions to be readily taken into account. The electrochemical potentials are used for the derivation of the equilibrium equations, ie the adsorption isotherms and the equation of state. A number of limiting cases of the multicomponent adsorption are briefly examined. The attention is focused on the effect of the specific adsorption of anions on the adsorption features of a neutral organic adsorbate. It is found that the theoretical predictions are in general agreement with experiment. The most interesting of the predicted properties is the increase in the adsorption of an organic adsorbate in the presence of adsorbed anions when the electrode charge density is used as the independent electrical variable. Indirect experimental evidences of this phenomenon are presented from literature and an explanation within the framework of our theory is given.