We discuss the fundamental processes including electron conduction and adhesion of metallic contacts pertaining to the scaling of the performance metrics of nano-electro-mechanical switches. In particular, we show that under most circumstances, the switching energy is governed by the force that is needed in order to break the electrical contact when opening the switch. For an optimally designed parallel plate capacitor switch, the energy consumption does not depend on the actuation voltage. However, stray capacitances degrade the energy efficiency if a high operating voltage is chosen. The limit is of the order of 1 V for an aggressively scaled Si device, for which an overall switching energy of the order of 150 eV, a footprint area of 2500 nm2 and a switching time of 200 ps are predicted. The scaling analysis also stipulates that materials with a low free electron density and high effective mass should be used for the electrical contact, which is counter-intuitive, as such materials are known to be poor conductors on the macroscopic scale. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.