  Theoretical descriptions for the nonleptonic decays of heavy flavour hadrons
have emerged that incorporate non-perturbative corrections in a systematic way
and are genuinely based on QCD. One can reproduce $\tau (D^+)/\tau (D^0)$,
$BR_{SL}(D^+)$ and $BR_{SL}(D^0)$ as due mainly to destructive interference in
$D^+$ decays; one predicts $\tau (B^-)$ to exceed $\tau (B_d)$ by a few per
cent; $BR_{SL}(B)$ is reduced only slightly, raising the prospects of a serious
and tantalizing conflict with ARGUS \& CLEO data. It is emphasized that the
lifetimes for the two mass eigenstates in the $B_s$-$\bar B_s$ system could
differ by 30\% or even more. The status of phenomenological treatments of
non-leptonic two-body modes is briefly reviewed.

High Energy Physics - Phenomenology