A short overview concerning the nature of the passive layer on iron will be given. It will be shown by the rotating split ring-disc technique that the experimental conditions, especially during the processes of Fe3O4 reduction, play an important role for the establishment of a "passive" layer model. The current efficiencies of various Fe3O4 reduction reactions will be discussed. During the electroreductive dissolution of iron oxides, clusters of Fe(II)oxy-hydroxides or hydroxylated Fe(II) ions leave the oxide surface.