  A critical review of the theoretical understanding of the lifetimes of beauty
hadrons is given. A model-independent analysis using the heavy-quark expansion
allows for a description of the lifetime ratios tau(B-)/tau(B0) and
tau(Lambda_b)/tau(B0) in a small region of parameter space. It is demonstrated
that the lifetime ratio tau(B-)/tau(B0) cannot be used to extract the decay
constant of the B meson. Implications for the semileptonic branching ratio and
charm yield in B decays are pointed out.
