This paper deals with the application of the most used surface analysis technique on materials characterization, X-ray photoelectron spectroscopy (XPS). This spectroscopic technique employs low energy electrons as probes, since their mean free paths in the solids are only few atomic layers. Technologically interesting processes, in which the physical and chemical properties of the topmost atomic layers of the materials play an important role, include heterogeneous catalysis, thin film growth, surface segregation, corrosion, and tribology. Examples will be presented on the surface characterization of oxide catalysts, thin metallic films, and thin oxide films (C) 2004 Elsevier B.V. All rights reserved.