The quest for the Cabibbo Kobayashi Maskawa Matrix

A piece of the Standard Model presently undergoing intense experimental scrutiny is the Cabibbo Kobayashi Maskawa matrix. Several different measurements are planned to enrich the spectrum of experimental constraints and thus provide one of the most stringent tests of Standard Model validity. The success of this program is closely related to theoretical progress in evaluating QCD matrix elements in a non-perturbative regime, as we need to extract fundamental quark properties from observations on decays involving hadrons. This interplay between experimental and theoretical progress will be illustrated in the context of the present knowledge of the magnitudes of the quark mixing parameters $| V_{cb}| $ and $| V_{ub}|$.