  In these lectures, I present several important applications of QCD sum rules
to the decay processes involving heavy-flavour hadrons. The first lecture is
introductory. As a study case, the sum rules for decay constants of the
heavy-light mesons are considered. They are relevant for the leptonic decays of
$B$-mesons. In the second lecture I describe the method of QCD light-cone sum
rules used to calculate the heavy-to-light form factors at large hadronic
recoil, such as the $B\to \pi \ell \nu_\ell$ form factors. In the third
lecture, the nonlocal hadronic amplitudes in the flavour-changing neutral
current decays $B\to K^{(*)}\ell\ell$ are discussed. Light-cone sum rules
provide important nonfactorizable contributions to these amplitudes.
