  Aspects of holography or dimensional reduction in gravitational physics are
discussed with reference to black hole thermodynamics. Degrees of freedom
living on Isolated Horizons (as a model for macroscopic, generic, eternal black
hole horizons) are argued to be topological in nature and counted, using their
relation to two dimensional conformal field theories. This leads to the
microcanonical entropy of these black holes having the Bekenstein-Hawking form
together with finite, unambigious {\it quantum spacetime} corrections. Another
aspect of holography ensues for radiant black holes treated as a standard
canonical ensemble with Isolated Horizons as the mean (equilibrium)
configuration. This is shown to yield a universal criterion for thermal
stability of generic radiant black holes, as a lower bound on the mass of the
equilibrium isolated horizon in terms of its microcanonical entropy. Saturation
of the bound occurs at a phase boundary separating thermally stable and
unstable phases with symptoms of a first order phase transition.
