Weak interactions of kaons from lattice QCD

The methods of lattice QCD and available computer resources are now sufficient that predictions for many of the Standard Model properties of kaons can be made from first principles with accurately bounded uncertainties. We discuss two relatively new areas where lattice methods are having or will soon have a large impact: calculation of the two complex amplitudes A₀ and A₂ describing the decay of the kaon into two-pions with I = 0 and 2 and calculation of long-distance contributions to second-order electro-weak processes including the K_L – K_S mass difference ΔM_K, the CP-violating parameter ε_K and certain rare kaon decays