Present theories of the capacity of the metal-electrolyte interface are discussed with particular emphasis on the contribution of the metal. A unified treatment of the interface is presented in which the potential distribution is calculated from nonlocal electrostatics. Two models are treated in detail: In the first model the boundary between the metal and the electrolyte is considered as sharp; it is shown that such a model is difficult to reconcile with the experimental data. The second model allows for the spill-over of the metal electrons into the solvent. Rough estimates show that this type of model is more in line with experimental results.