M-THEORY - STRINGS, DUALITY AND BRANES

String theory is an attempt to combine all of the known physical force s into a single unified framework. A powerful new type of duality symm etry has recently been discovered in string theory which has led to im portant breakthroughs. What were previously considered to be five dist inct string theories are now known to be different aspects of an under lying structure called M-theory. In addition to strings, extended obje cts of higher dimension or 'branes', play a key role. We review these developments and discuss the impact that they are having on quantum fi eld theory and the quantum properties of black holes.