ASPECTS OF N=1 STRING DYNAMICS

We review several topics of interest in the study of 4d N=1 supersymme tric compactifications of the heterotic string. After a brief introduc tion to the construction of such models, our focus is on the novel phy sics which occurs at singularities in the moduli space of vacua. Among the phenomena we discuss are nonperturbative superpotentials, dynamic al generation of poles in various low-energy couplings, and phase tran sitions which change the net number of chiral generations.