We review the relation between the Maldacena conjecture, also known as AdS=CFT correspondence, and the so-called holographic principle that seems to be an essential ingredient for a quantum gravity theory. We also illustrate the idea of holography by showing that the curvature of the anti-de Sitter space reduces the number of degrees of freedom making it possible to find a mapping between a quantum theory defined on the bulk and another defined on the corresponding boundary.