  In this talk I introduce the critical behavior occurring at the extremal
limit of black holes. The extremal limit of black holes is a critical point and
a phase transition takes place from the extremal black holes to their
nonextremal counterparts. Some critical exponents satisfying the scaling laws
are obtained. From the scaling laws we introduce the concept of the effective
dimension of black holes and discuss the relationship between the critical
behavior and the statistical interpretation of black hole entropy.
