The physical mechanisms that lead to the remarkable electron emission properties of single atom tips have been investigated. The primary tool used for this purpose has been large scale computer simulation. A simulation code has been developed to study a large variety of models. The simulation results have contributed significantly to the understanding of experimental findings. In particular it has been demonstrated that most of the features of the electron emission by these nanotips can be explained, at least qualitatively, in terms of the metal vacuum barrier. A computer animation movie, which provides a vivid demonstration of the effect of the various physical mechanisms on the properties of the emitted electron, has been produced.