The discovery and implications of the existence of two kinds of ion pairs in solutions of carbanion salts is described. Also discussed are the factors controlling tight-loose ion pair equilibrium: the nature of the carbanion and its counterion, temperature, pressure, solvent, and cation-complexing additives. A few examples are presented of the effect of these ionic species on the mechanisms of anionic polymerization and proton transfer. (C) 2004 Wiley Periodicals, Inc.