A unified model, embodying the induced density of interface states (IDIS) model, the reduction of the metal work function due to the adsorbed molecules ('pillow' effect) and molecular permanent dipoles, is presented for describing the barrier formation at metal/organic interfaces. While the IDIS model and 'pillow' effect have been described in previous approaches, in this paper we show how to introduce molecular permanent dipoles in the interface barrier formation. Examples for Au or Al/organic interfaces are discussed, which show the validity of our results and the generality of our formalism. (C) 2007 Elsevier B.V. All rights reserved.