  We review the Random First Order Transition Theory of the glass transition,
emphasizing the experimental tests of the theory. Many distinct phenomena are
quantitatively predicted or explained by the theory, both above and below the
glass transition temperature $T_g$. These include: the viscosity catastrophe
and heat capacity jump at $T_g$, and their connection; the non-exponentiality
of relaxations and their correlation with the fragility; dynamic heterogeneity
in supercooled liquids owing to the mosaic structure; deviations from the
Vogel-Fulcher law, connected with strings or fractral cooperative
rearrangements; deviations from the Stokes-Einstein relation close to $T_g$;
aging, and its correlation with fragility; the excess density of states at
cryogenic temperatures due to two level tunneling systems and the Boson Peak.
