DUALITY IN STRING THEORY

In these lectures we review some of the recent developments in string theory on an introductory and qualitative level. In particular we focu s on S - T - U dualities of toroidally compactified ten-dimensional st ring theories and outline the connection to M-theory. Dualities among string vacua with less supersymmetries in six space-time dimensions is discussed and the concept of F-theory is briefly presented.