  We introduce a new heterotic Standard Model which has precisely the spectrum
of the Minimal Supersymmetric Standard Model (MSSM), with no exotic matter. The
observable sector has gauge group SU(3) x SU(2) x U(1). Our model is obtained
from a compactification of heterotic strings on a Calabi-Yau threefold with Z_2
fundamental group, coupled with an invariant SU(5) bundle. Depending on the
region of moduli space in which the model lies, we obtain a spectrum consisting
of the three generations of the Standard Model, augmented by 0, 1 or 2 Higgs
doublet conjugate pairs. In particular, we get the first compactification
involving a heterotic string vacuum (i.e. a {\it stable} bundle) yielding
precisely the MSSM with a single pair of Higgs.
