K→Πνν and high precision determinations of the CKM matrix

We investigate the future determination of the CKM matrix using theoretically clean quantities, such as B(K⁺→Π⁺νν), B(K_L→Π⁰νν) or sin2β, sin2α as extracted from CP violation studies in B physics. The theoretical status of K→Πνν is briefly reviewed and their phenomenological potential is compared with that of CP asymmetries in B decays. We stress the unique opportunities provided by measuring the CP-violating rare decay K_L→Π⁰νν. It is pointed out that this mode is likely to offer the most precise determination of Im V^*_tsV_td and the Jarlskog parameter J_CP, the invariant measure of CP violation in the standard model.