The effect of barrier inelastic processes on the tunnel current is well understood, and has been successfully exploited as the technique of IETS. However, the case of electrode inelastic processes, despite its relevance to tunnelling in strong-coupling metals, magnetic systems, and even high- T c superconductors, has received much less attention. In this paper a simple model is presented to explain the effect of electrode phonons on the tunnel current, paying close attention to the physical processes involved. Although developed in terms of the electron-phonon interaction in a planar tunnel junction, it is applicable to a wider range of inelastic processes and also to other geometries, including the STM. The presence of electron-phonon coupling in one electrode has two consequences. Firstly it gives rise to an additional inelastic current. The ratio of the inelastic and unperturbed conductances is proportional to the imaginary part of the bulk electron-phonon self-energy. Secondly, the elastic current is altered, by modification of both the electronic density of states and the barrier penetration factor. These predictions are compared with experimental results from metal-insulator-metal tunnel junctions.