  Many extensions of the standard model, especially grand unified theories and
superstring models, predict the existence of additional Z' bosons and
associated exotic chiral supermultiplets. It has recently been argued that for
classes of string motivated models with supergravity mediated supersymmetry
breaking there are two scenarios for the additional Z's: either the mass is in
the accessible range < O(1 TeV), providing a natural solution to the mu problem
and implications for the Higgs and sparticle masses and for the LSP; or, when
the breaking is associated with a D-flat direction, at an intermediate scale,
providing a possible explanation for the hierarchies of quark and charged
lepton masses and new possibilities for neutrino masses. Related work,
examining the detailed structure of specific perturbative string vacua for D
and F-flat directions, surviving U(1)'s and exotics, and effective couplings,
is briefly described.
