Abstract Photoelectron spectroscopy (PES) has become an important tool in the study of surfaces and the solid state. This review discusses information obtained on the interaction of gases with metal surfaces. The fundamentals of electron spectroscopy are briefly reviewed and experimental methods outlined. Approaches to the interpretation of both X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectra (UPS) are discussed. The chemisorption of carbon monoxide is examined in detail, PES distinguishes two situations, where CO retains its molecular identity and where dissociation occurs. Bonding of the molecule is considered, as are factors affecting dissociation. Some XPS investigations of metal oxidation are examined and the significance of the several oxygen 1s peaks observed is discussed. The adsorption and decomposition of organic molecules has been studied primarily by UPS. Several investigations are summarized, and the decomposition of formic acid considered in detail. The application of electron excited Auger electron spectroscopy is briefly discussed.