An electron beam is directed at a surface. The electron scatters with an electron in the solid which is ejected from the material. The scattered electron and the ejected electron are detected simultaneously. This coincidence spectroscopy can be used to determine the energy and momentum of the ejected electron before the collision and hence provide a complete map of the electron density in momentum space. Electron enrgies are low and hence the technique is surface sensitive. EMS is also known as (e,2e) spectroscopy.