  Duality symmetries for strings moving in non-trivial spacetime backgrounds
are analysed. It is shown that for backgrounds generated from WZW and coset CFT
models such duality symmetries are exact to all orders in string perturbation
theory. Their implications for string dynamics in non-trivial/singular
spacetimes are discussed. (Talk given at the EPS 93 Conference, held at
Marseille, July 22-27. To appear in the Proceedings.)
