The events leading up to the discovery of crystalline - and -zirconium phosphates are described, along with a brief description of their structures and aqueous ion-exchange behavior. The recent assertion that in the emphase the protons are present as hydronium ions is refuted. A description of solid-solid ion exchange between -zirconium phosphate and anhydrous salts is presented, along with the implications of such reactions for soft chemical reactions. A brief description of solid-solid exchange applied to zeolites and to strong acid organic ion-exchange resins is also presented. 1993.