Electrochemical reduction of a wide variety of aromatic diazonium salts on carbon electrodes (glassy carbon, highly oriented pyrolytic graphite) leads to the covalent attachment of the corresponding aromatic radicals. The films thus deposited on glassy carbon surfaces require mechanical abrasion to be removed. Cyclic voltammetry, X-ray photoelectron spectroscopy, polarization modulation IR reflection absorption spectroscopy, Auger spectroscopy, and Rutherford backscattering spectroscopy allow the characterization of the overlayer and an estimate of the surface coverage. The latter can be controlled through diazonium concentration and electrolysis duration. The mechanism of derivatization is discussed on the basis of the kinetic data obtained from cyclic voltammetry and preparative electrolysis. This versatile method of surface modification may find applications in the field of carbon-epoxy composites as attested by the successful binding of grafted p-aminophenyl groups with epichlorhydrin.