The present paper discusses the role of the entropy of fusion vis-a-vis the phase transformation characteristics and the self-diffusion behavior of crystalline matrices. The data correlating the entropy of fusion with these properties in metals, alkali halides and some other inorganic compounds are presented and analyzed. It is shown that the occurrence of a solid-solid state phase transformation decreases the magnitude of the entropy of fusion. In addition, the self-diffusion rates within any class of solids scale inversely with the entropy of fusion. The functional relationship of the entropy of fusion vis-a-vis the compressibility and the volume expansion coefficient is also discussed. The conclusion is that the entropy of fusion is not just a physical parameter describing the energy changes associated with the melting. It is, in fact, related in a substantial manner to the bulk properties of the solid and controls the phase transition characteristics and self-diffusion behavior within any group or class of solids in a uniform and consistent manner. (C) 2004 Kluwer Academic Publishers.