In this article, we review recent progress in theoretical studies on the electronic properties of organic/metal interfaces, especially, on the origin of the interface dipoles. We first discuss the effect of the interface dipole on the charge injection barriers at organic/metal interfaces. Then, we observe the importance of the interface structure, especially, the organic-metal distances in physisorption systems. In this case, the experimentally observed substrate dependence of the interface dipole can be attributed mainly to the difference in the organic-metal distance. In the case of chemisorption systems, the induced density of interface states tends to pin the Fermi level relative to the HOMO and LUMO levels of molecules. We also discuss the importance of the alignment of molecular permanent dipoles in the case of Alq₃/metal interfaces, which are relevant to organic light emitting devices.