A Qcd Treatment of the Weak Decays of Heavy Flavour Hadrons – without Voodoo and Undue Incantations

There now exist several theoretical technologies for treating weak decays of heavy flavour hadrons that are genuinely based on QCD without having to invoke a deus ex machina. I focus on one of those, which employs an expansion in inverse powers of the heavy quark mass. It has developed into a rather mature framework incorporating many subtle aspects of quantum field theory. I describe its methodology for treating fully integrated decay rates as well as differential distributions, in particular energy spectra; the importance of a new type of sum rules, the SV sum rules, is emphasized. First practical benefits from this theoretical technology are listed, like predictions on lifetime ratios and extracting the KM parameter |V (cb)| from inclusive and from exclusive semileptonic B decays. An outlook is given onto future developments concerning the determination of the properly defined mass of the heavy quark and its kinetic energy and a reliable extraction of |V (ub)/V (cb)|. A few comments on charm decays are added. Invited Talk given at the International Workshop on B Physics, Nagoya, Japan, Oct. 26 28, 1994