  We present a simple proof of the WDVV equations for the prepotential of
four-dimensional N=2 supersymmetric Yang-Mills theory with all ADE gauge
groups. According to our proof it is clearly seen that the WDVV equations in
four dimensions have their origin in the associativity of the chiral ring in
two-dimensional topological Landau-Ginzburg models. The WDVV equations for the
BC gauge groups are also studied in the Landau-Ginzburg framework. We speculate
about the topological field theoretic interpretation of the Seiberg-Witten
solution of N=2 Yang-Mills theory.
