 Several of his papers from around this time study the connections between quantum field theory, knots, and Donaldson theory.He introduced the concept of a topological quantum field theory, inspired by Witten's work and Segal's definition of a conformal field theory.His book describes the new knot invariants found by Vaughan Jones and Edward Witten in terms of topological quantum field theories, and his paper with L. Jeffrey explains Witten's Lagrangian giving the Donaldson invariants.