  I review the QCD sum rules calculations of the form factors governing the
semileptonic decays of charmed and beauty mesons. In particular, I discuss the
predicted dependence of the various form factors on $q^2$ and how it can be
obtained for the form factors of vector and axial currents. In some cases the
$q^2$ dependence, computed by QCD sum rules, is different from the outcome of
lattice QCD. A Tau-Charm factory could be an efficient tool to study this
aspect of the charmed meson transitions.
