  Reduction of couplings in supersymmetric GUTs is achieved by searching for
renormalization group invariant (RGI) relations among couplings which hold
beyond the unification scale. Finiteness is due to the fact that there exist
RGI relations among couplings that guarantee the vanishing of the
beta-functions of a N=1 supersymmetric GUT even to all orders in perturbation
theory. Of particular interest are the relations among gauge and Yukawa
couplings which lead to very interesting predictions of the top quark mass
