  Polarization studies for heavy quarks can lead to important tests of the
Standard Model. Top quark pair production in $e^+e^-$ annihilation is
considered near energy threshold. It is shown that for longitudinally polarized
electrons the produced top quarks and antiquarks are highly polarized.
Dynamical effects originating from strong interactions in the $t-\bar t$ system
can be calculated using Green function method. Energy-angular distributions of
leptons in semileptonic decays of polarized heavy quarks are sensitive to both
the polarization of the decaying quark and V-A structure of the weak charged
current. Some applications to $b$ quark physics at the $Z^0$ resonance are
briefly reviewed.
