  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.
