The recent determination of the atomic structure of CdTe(110) and GaSb(110), and of GaAs(110)-In, GaAs(110)-Sb, and GaP(110)-Al has triggered a reevaluation of the atomic structures of compound semiconductor surfaces and interfaces. The atomic geometries of the (110) surfaces are dominated by a top bilayer bond rotation and a small contraction of the bilayer toward the substrate. The magnitude of the rotation angle approximately correlates with the lattice constant of the crystal. No simple correlation can be found between the surface relaxation and the ionicity of the crystal. The long range atomic structure of column III and V elements adsorbed on GaAs(110) and GaP(110) is evaluated, before and after annealing, in terms of adatom electronic configuration and interface reactivity. Column III elements form disordered overlayers whereas column V elements form ordered structures and modify the substrate relaxation. Annealing reactive interfaces (Al on GaAs and GaP) leads to a metal–cation replacement reaction and to the crystallization of a new compound. For unreactive interfaces (In and Sb on GaAs), annealing leads to the desorption of the column III metal (weak bonding) but demonstrates the strong bonding of Sb to the substrate. As expected, no replacement reaction is observed in these latter cases.