  We study the occurrence of critical phenomena in four - dimensional, rotating
and charged black holes, derive the critical exponents and show that they
fulfill the scaling laws. Correlation functions critical exponents and
Renormalization Group considerations assign an effective (spatial) dimension,
$d=2$, to the system. The two - dimensional Gaussian approximation to critical
systems is shown to reproduce all the black hole's critical exponents. Higher
order corrections (which are always relevant) are discussed. Identifying the
two - dimensional surface with the event horizon and noting that generalization
of scaling leads to conformal invariance and then to string theory, we arrive
to 't Hooft's string interpretation of black holes. From this, a model for
dealing with a coarse grained black hole quantization is proposed. We also give
simple arguments that lead to a rough quantization of the black hole mass in
units of the Planck mass, i. e. $M\simeq{1\over\sqrt{2}}M_{pl} \sqrt{l}$ with a
$l$ positive integer and then, from this result, to the proportionality between
quantum entropy and area.
