  We review the construction and classification of three-family grand unified
models within the framework of asymmetric orbifolds in perturbative heterotic
superstring. We give a detailed survey of all such models which is organized to
aid analysis of their phenomenological properties. We compute tree-level
superpotentials for these models. These superpotentials are used to analyze the
issues of proton stability (doublet-triplet splitting and R-parity violating
terms) and Yukawa mass matrices. To have agreement with phenomenological data
all these models seem to require certain degree of fine-tuning. We also analyze
the possible patterns of supersymmetry breaking in these models.
  We find that the supersymmetry breaking scale comes out either too high to
explain the electroweak hierarchy problem, or below the electroweak scale
unless some degree of fine-tuning is involved. Thus, none of the models at hand
seem to be phenomenologically flawless.
