Interfaces between dissimilar materials are critical to the performance of many electronic devices. In electrical devices where the active transport is through an organic semiconductor (OSC) layer there are metallic electrodes to supply and remove the charge carriers. At metal/molecule and molecule/metal interfaces the electrical contact is usually not Ohmic. As a result, in most metal-organic semiconductors–metal devices charge injection is mainly governed by tunneling across the barriers. When the metal electrodes are ferromagnetic the density of occupied and unoccupied electronic states is spin-dependent, which presents further subtleties to the electron transfer. In this article we summarize some of the important experimental results that have advanced our understanding of spin-polarized electron transfer across ferromagnetic metal (FM)/OSC interfaces. In particular, we highlight key spectroscopic studies that have revealed insights into the nature of the electronic structure between OSCs and FMs, in particular between Alq3 and Co and Fe surfaces. We discuss the relationship between energy level diagrams for these systems and transport measurements made on spin-valve devices.