  AdS/CFT-correspondence establishes a relationship between supersymmetric
gravity (SUGRA) on Anti-de-Sitter (AdS) space and supersymmetric Yang-Mills
(SYM) theory which is conformaly invariant (CFT). The AdS space is the solution
of the Einstein-Hilbert equations with a constant negative curvature. Why is
this relationship important? What kind of relationship is this? How does one
find it? The purpose of this text is to answer these questions. We try to
present the main ideas and arguments underlying this relationship, starting
with a brief sketch of old string theory statements and proceeding with the
definition of D-branes and a description of their main features. We finish with
the observation of the correspondence in question and the arguments that favor
it.
