Some theories and concepts regarding current efficiency (CE) in aluminium reduction cells are reviewed. The Sterten-Solli model, which represents the current understanding, explains the CE loss as a result of the formation of dissolved metal at the cathode, notably sodium. Sodium is transported into the electrolyte across the boundary layer at the cathode, "stealing" electrons that would otherwise be used in the main cathode reaction. While dissolved species may be transported by ordinary mass transfer; it is also known that cryolitic melts containing dissolved metal exhibit electronic conductivity. The main content in the present paper is an attempt to separate between CE loss by ordinary mass transfer and CE loss by electronic conduction, and to explain the relationship between the two. This constitutes the basis for a new "integrated" CE model, which apparently implies a weaker relationship between CE and convection than what can be calculated by ordinary mass transfer.