  Over the last few years a theoretical treatment for the weak decays of
heavy-flavour hadrons has been developed that is genuinely based on QCD. Its
methodology is described as it applies to total lifetimes, and the underlying
theoretical issues are discussed. Theoretical expectations are compared with
present data. One discrepancy emerges: the beauty baryon lifetime appears to be
significantly shorter than predicted. The ramifications of those findings are
analyzed in detail, and future refinements are described.
