In product engineering of particulate systems, the property function relates the dispersity to the product properties, whereas the process function shows how to produce the required dispersity. These principles are applied to the production of nanoparticles. Nanoparticles are controlled by surface forces. Due to their high mobility nanoparticles are unstable and may coagulate rapidly if the particles are not stabilized. Stabilization is achieved by tailoring the particulate surfaces, e.g. through repulsive double layer forces. Macroscopic properties are thus controlled by microscopic control of the interfaces, i.e. we bridge the gap between the molecular level and material properties. These principles are generally valid and are thus applied to precipitation and to nanomilling in stirred ball mills. The mean particle size in precipitation can be controlled by either the mixing intensity or the surface charge density of the particles. In stirred media mills oxide particles as small as 10 nm can be achieved by stabilizing the particles appropriately. (C) 2004 Elsevier B.V. All rights reserved.