Copper in aqueous sulphuric acid solution at room temperature displays a low level active (metastable) surface state redox transition well within the double layer region, at ca. -0.7 +/- 0.1 V (SMSE). The latter is an important feature of this electrode system as it apparently coincides with (a) the transition from activation to transport control in acid sulphate copper plating baths, (b) a major change in the inhibiting properties of several plating bath additives, and (c) the onset/termination potential of electrocatalytic processes, e.g. nitrate reduction, at copper in acid. The nature and influence of this active surface state behaviour, which is assumed to be relevant to Damascene copper plating, is discussed.