A new definition for the absolute half-cell potential is proposed. An absolute half-cell process is first defined. The absolute half-cell potential is ∆G for that process. (The conversion from energy to voltage is done in the usual way by using Faraday's constant.) Under this definition the complete thermodynamic states of all species including electrons taking part in an absolute half-cell reaction must be fully specified. This is a departure from earlier treatments and makes it possible to develop a complete and consistent theory of absolute half-cell thermodynamics. Differences between the present approach and earlier treatments are discussed. Determination of ∆G0 is briefly discussed, as well as possible uses for absolute half-cell thermodynamics, particularly in relation to the thermodynamics of ion solvation.