  We analyze gauge coupling unification in the context of heterotic strings on
anisotropic orbifolds. This construction is very much analogous to effective 5
dimensional orbifold GUT field theories. Our analysis assumes three fundamental
scales, the string scale, $\mstring$, a compactification scale, $\mc$, and a
mass scale for some of the vector-like exotics, $\mex$; the other exotics are
assumed to get mass at $\mstring$. In the particular models analyzed, we show
that gauge coupling unification is not possible with $\mex = \mc$ and in fact
we require $\mex \ll \mc \sim 3 \times 10^{16}$ GeV. We find that about 10% of
the parameter space has a proton lifetime (from dimension 6 gauge exchange)
$10^{33} {\rm yr} \lesssim\tau(p\to \pi^0e^+) \lesssim 10^{36} {\rm yr}$. The
other 80% of the parameter space gives proton lifetimes below Super-K bounds.
The next generation of proton decay experiments should be sensitive to the
remaining parameter space.
