  A review of orbifold geometry is given, followed by a review of the
construction of four-dimensional heterotic string models by compactification on
a six-dimensional Z_3 orbifold. Particular attention is given to the details of
the transition from a classical theory to a first-quantized theory.
Subsequently, a discussion is given of the systematic enumeration of all
standard-like three generation models subject to certain limiting conditions.
It is found that the complete set is described by 192 models, with only five
possibilities for the hidden sector gauge group. It is argued that only four of
the hidden sector gauge groups are viable for dynamical supersymmetry breaking,
leaving only 175 promising models in the class. General features of the spectra
of matter states in all 175 models are discussed. Twenty patterns of
representations are found to occur. Accomodation of the Minimal Supersymmetric
Standard Model (MSSM) spectrum is addressed. States beyond those contained in
the MSSM and nonstandard hypercharge normalization are shown to be generic,
though some models do allow for the usual hypercharge normalization found in
SU(5) embeddings of the Standard Model gauge group. Only one of the twenty
patterns of representations, comprising seven of the 175 models, is found to be
without an anomalous U(1). Various quantities of interest in effective
supergravity model building are tabulated for the set of 175 models. String
scale gauge coupling unification is shown to be possible, albeit contrived, in
an example model.
