The dissolution of goethite in aqueous media containing EDTA, Fe(II), and Fe(III) has been studied. The main dissolution pathways involve the inner or outer sphere electron transfer in mixed-valence EDTA-bridged surface complexes and in surface "ion pairs." A synergistic effect is observed between ferrous EDTA and free EDTA. The rate dependencies on [EDTA] and [Fe-II] are interpreted in terms of Fe(II) phase transfer from three different surface complexes : =Fe-III-Y-Fe-II (Y is the EDTA anion), =Fe-III-Y ... (FeY)-Y-II, and the dimeric species with adjacent sites =Fe-III-Y and =Fe-III-Y-Fe-II. Addition of iron(III) produces a rate decrease that is explained on the basis of the adsorption behavior of (FeY-)-Y-III, for which adsorption data are presented. The redox equilibration of the surface is discussed.