Lattice QCD, OPE and the standard model

A number of old and new methods for computing K --> pi pi amplitudes on the lattice are reevaluated. They all involve a non-perturbative determination of matching coefficients, I will show how problems related to operator mix ing can be greatly reduced by introducing the O.P.E. of hadronic currents d irectly on the lattice. Applications to the evaluation of CP-symmetric (Del ta I = 1/2 rule) and CP-violating (epsilon'/epsilon) processes are presente d.