The use of nonaqueous solvents as media for chemical reactions has developed rapidly in the last 20 years. Prior to that time only scattered explorations of solvent-solute effects had been reported, and still fewer investigations of the effects of solvents on equilibria and reaction rates had been made. Classic pioneering studies include the conductance work in organic solvents of P. Walden, C. A. Kraus, and their co-workers early in the century (a single paper by Walden and Birr reported conductance data on 35 salts in acetonitrile), and the work in inorganic solvents by L. Audreith in the 1930's. These early studies of the physical properties of the solvents and their solutions did not trigger much response, perhaps in part because of difficulties associated with purification of the solvents, and also because there seemed to be no particular advantage to the replacement of water as solvent for most applications. Besides, much remained to be learned about aqueous solutions and water itself (this is still true today).