The electronic structure at the interface formed between an organic film and a metal electrode plays a crucial role in the performance of electronic devices using organic semiconductors such as electroluminescent displays (light-emitting diodes), field-effect transistors, and photovoltaic cells. In particular, the energies of the highest-occupied and lowest-unoccupied molecular orbitals relative to the Fermi level of metals, i.e., the energy level alignment at organic/metal interfaces, are of fundamental importance in discussing the barrier heights for the charge injection and separation at the interface. However, it is generally not easy to discuss the interfacial electronic structure precisely since the interface energetics is usually modified due to various interface-specific phenomena. In this article, we introduce the recent progress in studies of the energy level alignment at organic/metal interfaces: (1) basic understanding, (2) interface dipole layer, and (3) interface states.