X-ray photoelectron spectroscopy (XPS) is a widely used method in fundamental surface science and applied materials characterization. As an analytical technique, XPS is an integral part of a modern materials research laboratory. Characterization of complex materials usually requires combinations of analytical methods to provide an understanding of structure-property relationships. In this talk, I will review the types of information provided uniquely by XPS, and illustrate how this information is coupled with data provided from other methods in the characterization of surfaces and thin films. Some examples will be selected from the author's own experience as an XPS expert within a larger materials characterization group at a major industrial R&D site. In this setting, a wide variety of sample types and issues are encountered. The variable degrees of success in the application of XPS to quantitative analysis, determination of oxidation states and functional groups, and thin film compositions will be described. In addition, the current and prospective applications in emerging fields such as biotechnology and nanotechnology will be discussed.