  The recent LEP data for gauge coupling constants constrain many grand unified
models. In this paper, we study several possibilities for unification of gauge
coupling constants. Without an intermediate mass scale, the minimal
supersymmetric standard model is the only possibility. For one intermediate
mass scale, it is possible to have many routes toward grand unification:
$SO(10)\rightarrow SU(3)_c\times SU(2)_L\times SU(2)_R\times U(1) , SU(7),
SU(8)$, etc. We present also simple relations for the possibility of
unification.
