The adsorption of polyethylene glycol (PEG) on Au(111) for three different molar masses was studied by cyclic voltammetry, capacity measurements, and in situ scanning tunneling microscopy for the first time. New physical insight into the adsorption behavior of this polymer on a solid electrode in neutral Na2SO4 was gained. The formation of a condensed phase has been observed, the stability range depending strongly on the chain length and the concentration of PEG. Because of their importance in electroplating the influence of chloride ions on the PEG adsorption behavior has also been investigated, together with the effect of PEG and chloride on the initial stages of Cu deposition. Addition of chloride does not lead to an increased adsorption of PEG as found for other surfaces (e.g., copper), but to a simple superposition of both adsorption processes. However, a strong inhibition for copper bulk deposition is observed when both additives are present in solution. (C) 2004 The Electrochemical Society.