  I discuss the construction of realistic superstring standard--like models in
the four dimensional free fermionic formulation. I discuss the massless
spectrum of the superstring standard--like models and the texture of fermion
mass matrices. These models suggest an explanation for the top quark mass
hierarchy. At the cubic level of the superpotential only the top quark get a
mass term. The lighter quarks and leptons obtain their mass terms from
nonrenormalizable terms that are suppressed relative to the cubic order term. A
numerical estimate yielded $m_t\sim175-180~GeV$. The suppression of the
lightest generation masses results from the horizontal symmetries in the
superstring models. The problems of neutrino masses, gauge coupling unification
and hierarchical SUSY breaking are discussed. I argue that the realistic
features of these models are due to the underlying $Z_2\times Z_2$ orbifold,
with standard embedding, at the free fermionic point in toroidal
compactification space.
