The concept of glassy crystals and some of the recent examples are reviewed here to emphasise the wide occurrence of glass transition phenomena in condensed matters not only in liquids but also in crystals. It became apparent that the glass transition is essentially associated with the 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 irrespective of the translational periodicity of the constituent entities. A general relation between the dielectric relaxation and glass transition is considered.