  The status of coupling constant unification (with and without a unification
of Yukawa couplings) is discussed. Uncertainties associated with the input
coupling constants, $m_{b}$ and $m_{t}$, threshold corrections at the low and
high scale, and possible nonrenormalizable operators are described and a
discrepancy between effective and physical scales is pointed out. Theoretical
uncertainties in the predictions of $\alpha_{s}(M_{Z})$, $m_{b}$, and the
unification scale, $M_{G}$, are discussed and estimated. Constraints on the
super-partner spectrum are found to be weak if uncertainties associated with
the high-scale are included. However, requiring $h_{b} = h_{\tau}$ at $M_{G}$
excludes $3 < \tan \beta < 40$ (for $m_{t} < 200$ GeV).
