Research during the last decade has led to the microscopic understanding of the atomic, electronic, and chemical (compositional) structures at semiconductor surfaces and interfaces. First, we present a brief review of LEED (Low energy Electron Diffraction) intensity analyses of the atomic geometry of the (110) surfaces of 3-5 and 2-6 compounds. The dynamical calculation proposes an atomic model of the (110) surface with top twolayer reconstructions for GaAs, InSb, InP, and probably the topmost singlelayer reconstruction for the more ionic ZnTe. Secondly, after a brief description of standard AES analyses of the chemical composition of the surfaces and interfaces, particular attention is focussed on soft Xray photoemission studies on the interface formed by MBE (Molecular Beam Epitaxy) techniques. Thirdly, theoretical band calculations are mentioned based on the LEED atomic model. Finally, to develop a model of the atomic geometry and the initial step of oxidation. we present recent ab initio first principle calculations using a technique of quantum chemistry which has been applied to the GaAs (110) surface.