The morphology of iron oxides and oxohydroxide particles grown from aqueous solution reflects the crystallographic properties of the small crystallites that compose the particles, the characteristics of the crystallite aggregation process that leads to the observed particles, and the composition of the mother solution. The shapes and sizes of alpha-FeOOH, gamma-FeOOH, and Fe3O4 grown from aqueous solution under a variety of conditions are described and explained on the basis of these three factors.