Two Dimensional Gauge Theories Revisited
  Topological gravity is equivalent to physical gravity in two dimensions in a way that is still mysterious, though by now it has been proved by Kontsevich. In this paper it is shown that a similar relation between topological and physical Yang-Mills theory holds in two dimensions; in this case, however, the relation can be explained by a direct mapping between the two path integrals. This (1) explains many strange facts about two dimensional Yang-Mills theory, like the way the partition function can be expressed exactly as a sum over classical solutions, including unstable ones; (2) makes the corresponding topological theory completely computable. 
Edward Witten