  We discuss some aspects of perturbative $(0,2)$ Calabi-Yau moduli space. In
particular, we show how models with different $(0,2)$ data can meet along
various sub-loci in their moduli space. In the simplest examples, the models
differ by the choice of desingularization of a holomorphic V-bundle over the
same resolved Calabi-Yau base while in more complicated examples, even the
smooth Calabi-Yau base manifolds can be topologically distinct. These latter
examples extend and clarify a previous observation which was limited to
singular Calabi-Yau spaces and seem to indicate a multicritical structure in
moduli space. This should have a natural F-theory counterpart in terms of the
moduli space of Calabi-Yau four-folds.

High Energy Physics - Theory