We summarize recent results on QCD corrections to various
observables in semileptonic $b$ quark decays. For massless leptons in
the final state we present effects of such corrections on triple
differential distribution of leptons which are important in studies of
polarized $b$ quark decays. Analogous formulas for distributions of
neutrinos are applicable in decays of polarized $c$ quarks. In the
case of decays with a $\tau$ lepton in the final state mass effect of
$\tau$ has to be included. In this case we concentrate on corrections