Measurements of the kinetics and the flux of copper ions to an electrode surface by means of a rotating ring-disk electrode (RRDE) are employed for the first time in a study of the underpotential (UPD) and overpotential (OPD) deposition of copper on a Pt(111) disk electrode. The RRD(Pt(111))E measurements presented here show definitively that, in the presence of chloride, Cu UPD is a two-stage process, both of them involving Cu deposition. The coverage of Cu and Cl after the first stage of UPD is ca. 0.58 ML (ML = monolayer). There is little or no additional adsorption of chloride ion during the initial stage of Cu UPD. The second stage of Cu UPD is primarily related to the deposition of Cu forming an essentially complete monolayer (approximate to 0.9 ML), accompanied by desorption of approximately 0.1 ML of Cl-. In pure perchloric acid, Cu electrodeposition is a slow, kinetically controlled process. The presence of either (bi)sulfate and/or chloride in the electrolyte significantly enhances the kinetics of Cu deposition. This enhancement is suggested to be related to the tendency of large anions to perturb the solvation shell of strongly hydrated Cu2+ ions. In electrolyte with 10(-2) M Cl-, Cu2+ is partially reduced to Cu+ in the vicinity of the OPD potential region due to its complexation with Cl-. The observed potential regions of stability for Cu2+, Cu+, and Cu-0 were confirmed by a thermodynamic analysis.