Abelian and Non-Abelian Dualities in String Bacgrounds

We present a brief discussion of recent work on duality symmetries in non-trivial string backgrounds. Duality is obtained from a gauged non-linear sigma-model with vanishing gauge field strength. Standard results are reproduced for abelian gauge groups, whereas a new type of duality is identified for non--abelian gauge groups. Examples of duals of WZW models and 4-d black holes are given. (Presented at `From Superstrings to Supergravity', Erice 1992)