Transparent electronics employs wide band gap semi-conductors which are transparent in the visible portion of the electromagnetic spectrum for the fabrication of electronic devices and circuits. Current and future transparent electronics applications require the use of wide band gap oxide semi-conductor interfaces as contacts and rectifiers, as well as for passivation and barrier-shaping layers. Modem Schottky barrier and heterojunction theory can be applied to the assessment of such interfaces, and is reviewed for this purpose from a charge transfer, energy band diagram perspective. Ideal interface formation theory is envisaged as originating from Fermi level mediated charge transfer giving rise to a macroscopic interfacial dipole, while non-ideal theory involves charge neutrality level mediated charge transfer giving rise to a microscopic interfacial dipole. This interface formation theory is applied to the problem of indium tin oxide (ITO) - zinc oxide and ITO -tin oxide interfaces, confirming their utility as injecting source-drain contacts in transparent thin-film transistors. (c) 2007 Elsevier B.V. All rights reserved.