  A method is presented by which a hidden N=2 superconformal symmetry can be
exhibited in a string theory or indeed in a topological conformal field theory.
More precisely, we present strong evidence, based on calculations with string
theories, in favour of the conjecture that any topological conformal field
theory can be obtained by twisting an N=2 superconformal field theory. (Talk
given at the Workshop on Gauge Theories, Applied Supersymmetry and Quantum
Gravity held at Imperial College, London, 5-10 July 1996.)
