Add to ORKGpublisher[Abstract] The concept of glassy crystals and its thermodynamic consequence are described briefly. Some recent examples of the glassy crystals are reviewed here to emphasize the wide occurrence of glass transition phenomena in condensed matters not only in liquids but also in crystals. It turned out that the glass transition is essentially associated with freezing-in process of any degrees of freedom that a system possesses. The glass transitions which have been observed so far are just one example of the transitions that must be of wide occurrence in solids irrespectively of the translational periodicity of the constituent entities. General relation between the dielectric relaxation and glass transition is considered