Lattice calculations for B and K mixing

The bag parameters and the decay constants of neutral B(s)and K mesons were among the non-perturbative hadronic inputs to the classical CKM Unitarity Triangle Analysis. Thanks to the big amount of experimental information collected in the last few years at the B-factories and by the CDF collaboration, these matrix elements are now among the outputs of the unitarity fits, once the validity of the Standard Model has been postulated. Lattice calculations of the mixing amplitudes are still needed in order to make a test of the theory, provided that their statistical and systematic errors are under control at the level of a few percent. Here we review some of the recent lattice calculations of these quantities.