  In this thesis the research work, done by the author in the three years of
his Ph.D. study, will be exposed. The role of two dimensional conformal field
theories will be discussed. Different approaches will be studied in order to
find a classical central charge in the Poisson algebra of the symmetry
generators. In this way one can compute the black hole entropy using the Cardy
formula. Being the central charge classical the computation is independent from
a specific model of quantum theory of gravity. It will be shown eventually that
the microscopic degrees of freedom of the black hole can be described by a free
field and some considerations on a possible quantization of the theory will be
made.
