The scope of this review includes studies on the hydrolysis and precipitation of Fe(III) from aqueous solutions of its inorganic salts, chiefly the nitrate, perchlorate, chloride, and sulfate. After a survey of structural and thermodynamic properties of the relevant Fe(III) species, this review examines the reactions of hydrolysis and precipitation in aqueous Fe(III) solutions. These reactions, most of which occur slowly, include the formation, aging, and agglomeration of a red cationic hydrolytic polymer. The constitution of the slowly precipitated hydrous oxide products is also examined. For comparison, the constitution and aging of rapidly precipitated hydrous iron(III) oxides is briefly surveyed. Techniques employed in the study of Fe(III) hydrolysis and precipitation include ph measurement, visible and infrared spectroscopy, ultracentrifugation, electron microscopy, and x-ray diffraction. Electrokinetic properties and thermal dehydration of precipitated iron oxides are not considered. Iron(III) oxides, hydrous oxides, or related compounds formed via oxidation of elemental iron or iron(II) compounds, or via other redox reactions, are not considered.