Surface physics and chemistry have in recent years become one of the most active fields in solid state research. A number of techniques have been developed, and both the experimental aspect and the correlated theory are evolving at an extremely fast rate. Electron and ion spectroscopy are of major importance in this development. In this volume, which contains edited and extended versions of eight sets of lectures given at the NATO Advanced Study Institute held at Ghent, Belgium, from August 29 to September 9, 1977, a re­ view of the state of the art in these fields is given from both an experimental and a theoretical point of view. Electron emission techniques such as UPS (ultraviolet photoemission spectroscopy), XPS (x-ray photoemission spectroscopy), and AES (Auger electron spectroscopy) constitute the major part of this volume, reflecting the fact that they continue to be the most widely applied surface techniques. Recent developments in the application of synchrotron radiation to angle-resolved photoelectron spectroscopy are extensively covered, from an experimental point of view by Prof. W. E. Spicer (Stanford University, U.S.A.) and from a theoretical point of view by Dr. A. Liebsch (Kernforschungsanlage Julich, Germany). Emphasis is put on the study of energy bands in layered structures, and on chemisorption on well-defined surfaces. Chemisorption and catalysis on metals is treated in detail by Prof. G. Ertl (Universitat Munchen, Germany). This chapter contains a review of the application of the different surface techniques to specific surface systems.