The current status of the theory and phenomenology of weak decays of hadrons
containing a heavy quark is reviewed. Exclusive semileptonic and rare decays of
B mesons are discussed, as well as inclusive decay rates, the semileptonic
branching ratio of the B meson, and the lifetimes of b-flavoured hadrons.
Determinations of αs from Υ spectroscopy are briefly
presented.Comment: 27 pages, 7 figures, discussion of the theory of the B semileptonic
branching ratio has been revise