The glass transition phenomena are observed in many different classes of materials and have been studied in various disciplines. It is a long-standing problem due to the increasing number of important and general experimental facts that challenge conventional theories to explain. A collection of such experimental facts on the structural relaxation is given here, together with the observation that they are either governed by or correlated with the time/frequency dispersion of the structural relaxation. There is a class of secondary relaxations (named after Johari-Goldstein (JG)) that are well-connected to the structural relaxation in many ways. Thus, a fully successful theory of glass transition must take into consideration the roles played by the dispersion of the structural relaxation and the JG secondary relaxation. The results from our study of mixtures of van der Waals liquids are presented to illustrate these points, and a satisfactory explanation of the data is given. The understanding of the component dynamics gained from the study of these ideal systems is used to elucidate and interpret the experimental data of aqueous mixtures and hydrated proteins, which are more complicated systems. This exercise illustrates the benefit of broadening the study of one class of glass-forming materials to another class normally investigated by workers in another discipline.