This monograph deals with structural and electronic properties of semiconductor surfaces and interfaces. The first part of the text introduces the general aspects of space-charge layers, of clean-surface and adatom-included surfaces states, and of interface states. It is followed by a presentation of experimental results on clean and adatom-covered surfaces, which are explained in terms of simple physical and chemical concepts and models. Where available, results of more refined calculations are considered. A final chapter is devoted to the band line-up at semiconductor interfaces.