  We review the possibility that the Supersymmetric Standard Model arises from
orbifold constructions of the E_8 x E_8 Heterotic Superstring, and the
phenomenological properties that such a model should have. In particular,
trying to solve the discrepancy between the unification scale predicted by the
Heterotic Superstring (g_{GUT}x5.27x10^{17} GeV) and the value deduced from LEP
experiments (2x10^{16} GeV), we will predict the presence at low energies of
three families of Higgses and vector-like colour triplets. Our approach relies
on the Fayet-Iliopoulos breaking, and this is also a crucial ingredient,
together with having three Higgs families, to obtain in these models an
interesting pattern of fermion masses and mixing angles at the renormalizable
lebel. Namely, after the gauge breaking some physical particles appear combined
with other states, and the Yukawa couplings are modified in a well controlled
way. On the other hand, dangerous flavour-changing neutral currents may appear
when fermions of a given charge receive their mass through couplings with
several Higgs doublets. We will address this potential problem, finding that
viable scenarios can be obtained for a reasonable light Higgs spectrum.
