The work function of a surface is one of its most basic and influential features. It has long been recognized that work function controls thermionic and field emission. The work function of a solid surface affects charge transfer to or from an adsorbate. It influences the electron tunneling probability between surfaces. It plays a role in quantization of electron states parallel to the surface in metal-supported metallic nanoislands. There is also evidence linking the work function of a metal surface to its friction coefficient.