The precipitation technique is probably the simplest and most efficient chemical pathway to obtain iron oxide particles. Iron oxides (FeOOH, Fe3O4 or γ-Fe2O3) are usually prepared by addition of alkali to iron salt solutions and keeping the suspensions for ageing. The main advantage of the precipitation process is that a large amount of nanoparticles can be synthesized. However, the control of particle size distribution is limited, because only kinetic factors are controlling the growth of the crystal.