It is assumed in the electric field theory of toner charging that toner particles triboelectrically charge until a material-dependent electric field is created at the surface of each toner particle. This is also called the high-density limit of the surface state theory. There are now two independent published experimental tests that are consistent with this theory. These experimental tests are reviewed and analyzed. In addition, several topics related to this theory are discussed, including (1) progress towards a microscopic theory of toner charging, (2) limitations on one of the theories of toner adhesion, and (3) a proposed new theory of the source of wrong sign toner.