Conjugated organic materials are being increasingly incorporated in devices such as solar cells. In the operation of such devices, electron-transfer processes play a key role. Also, there is high current interest in the characterization of self-assembled monolayers (SAMs) on the surfaces of noble metal or (transparent) conducting oxides such as ITO. In order to tune the interface properties and to endow the self-assembled systems with functionality suitable for use in either macroscopic or nanoscale devices, the use of pi-conjugated molecules is promising. The first part of this presentation focuses on a theoretical description of charge-separation phenomena at organic-organic interfaces. Our approach is based on electron-transfer theory, which provides a molecular, chemically-oriented understanding. The second part deals with a theoretical description of the electronic structure of the interface between metallic or conducting oxide substrates and covalently-bound organic semiconductors. Of interest is the modification of the substrate workfunction upon SAM formation.