Abstract A qualitative and quantitative study of the title system was carried out by cyclic voltammetry and surface Raman spectroscopy. The Raman spectra of phenanthroline species can be observed at the electrode/electrolyte interface. With KNO 3 as an electrolyte, a weak Raman sepctrum of adsorbed phenanthroline is observed on polished electrodes before any oxido-reduction cycle is performed. Subsequent cycles do not modify the system significantly. With KCl as an electrolyte, electrochemical and Raman spectroscopic proofs are given of the interfacial occurence, with cycling, of both phenanthroline and an inner-sphere complex Ag(phen) x Cl ( x probably 2, E°′ = −0.17 V/SCE). The electrochemical behaviour of this complex and of Ag(phen) 2NO 3,H 2O and Ag(phen)NO 3, either deposited on inert electrodes immersed in aqueous KCl or as solutes in dimethylformamide solutions, was studied; for all three complexes, the same two redox Ag I Ag 0 reactions occur. Formation of surface carbon, due to the carbonization of part of the phenanthroline, is observed; it takes place during the Ag 1Ag 0 oxido-reduction process. The possible carbonization and SERS mechanisms are discussed.