The observation here that conventional aqueous standard potentials based on that of the standard hydrogen electrode (SHE) vary linearly with the gaseous ionization potentials for many groups of elements has enabled obtaining the absolute potential of the SHE and thereby the absolute aqueous standard potentials of elements. Depending on the slopes of the lines, redox couples have been classified into several aqueous groups. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3186645] All rights reserved.