Numerous products (such as paints, inks, foods, and beverages) and processes (such as coating, coagulation, sedimentation, lubrication, and paper-making) depend on the stability of the liquid films separating the dispersed phase from the continuous phase in the presence of nanoparticles or surfactant micelles. Nanoparticles exhibit a tendency to form ordered layers (i.e., stratification) and particle in-layer structures in these thin films at a sufficiently high concentration, resulting in a structural force that stabilizes the dispersion. The dispersion stability depends on the film size and the nanoparticle concentration. (C) 2003 Elsevier Inc. All rights reserved.