DUALITY OF (0,2) STRING VACUA

We discuss a duality of (0,2) heterotic string vacua which implies tha t certain pairs of (0,2) Calabi-Yau compactifications on topologically distinct target manifolds yield identical string theories. Some compl ex structure moduli in one model are interpreted in the dual model as deforming the holomorphic structure of the vacuum gauge bundle (and vi ce versa). A better understanding of singularity resolution for (0,2) models may reveal that this duality of compactifications on singular s paces is part of a larger story, involving smooth topology-changing pr ocesses which interpolate between the (0,2) models on the resolved spa ces.