On Associativity Equations

We consider the associativity or Witten-Dijkgraaf-Verlinde-Verlinde (WDVV) equations and discuss one of the most relevant for non-perturbative physics class of their solutions based on existence of the residue formulas. It is demonstrated for this case that the proof of associativity equations is reduced to the problem of solving system of algebraic linear equations. The particular examples of solutions related to Landau-Ginzburg topological theories, Seiberg-Witten theories and tau-functions of quasiclassical hierarchies are discussed in detail. We also discuss related questions including covariance of associativity equations, their relation to dispersionless Hirota relations and auxiliary linear problem for the WDVV equations.