  These TASI lectures review the Holographic principle. The first lecture
describes the puzzle of black hole information loss that led to the idea of
Black Hole Complementarity and subsequently to the Holographic Principle
itself. The second lecture discusses the holographic entropy bound in general
space-times. The final two lectures are devoted to the ADS/CFT duality as a
special case of the principle. The presentation is self contained and
emphasizes the physical principles. Very little technical knowledge of string
theory or supergravity is assumed.
