  We give a brief review of the AdS/CFT correspondence, which posits the
equivalence between a certain gravitational theory and a lower-dimensional
non-gravitational one. This remarkable duality, formulated in 1997, has sparked
a vigorous research program which has gained in breadth over the years, with
applications to many aspects of theoretical (and even experimental) physics,
not least to general relativity and quantum gravity. To put the AdS/CFT
correspondence in historical context, we start by reviewing the relevant
aspects of string theory (of which no prior knowledge is assumed). We then
develop the statement of the correspondence, and explain how the two sides of
the duality map into each other. Finally, we discuss the implications and
applications of the correspondence, and indicate some of the current trends in
this subject. The presentation attempts to convey the main concepts in a simple
and self-contained manner, relegating supplementary remarks to footnotes.
