  I discuss the heavy quark expansion for the inclusive widths of heavy-light
hadrons, which predicts quite well the experimental ratios of B_q meson
lifetimes. As for $\Lambda_b$, current determinations of ${\cal O}(m_b^{-3})$
contribution to $\tau(\Lambda_b)$ do not allow to explain the small measured
value of $\tau(\Lambda_b)/\tau(B_d)$. As a final topic, I discuss the
implications of the measurement of the B_c lifetime.
