  In this talk we review the theoretical status of the lifetime ratios of heavy
hadrons and of the B-mixing quantities $\Delta M_s$, $\Delta \Gamma_s$ and
$\phi_s$. While $\Delta M_s$ and $\Delta \Gamma_s$ suffer from large
uncertainties due to the badly known decay constants, the ratio $\Delta
\Gamma_s / \Delta M_s$ can be determined with almost no non-perturbative
uncertainties, therefore it can be used to look for possible new physics
effects.
