I will describe the AdS/CFT correspondence concentrating on its quantum aspects. I will briefly review what a quantum field theory is, and how through the AdS/CFT correspondence it is related to a quantum theory of gravity. In particular I shall describe why physicists are excited by the correspondence, and what they hope to learn. I will also try to describe in which limits the geometric aspects of AdS-CFT (to be reviewed in the previous talk) become relevant.