Theoretical results are presented for top quarks
produced in annihilation of polarized electrons
on positrons. Polarization studies for $t\bar t$
pairs near threshold are free from hadronization ambiguities.
This is due to the short lifetime of the top quark.
Semileptonic decays are discussed as well as their
applications in studying polarization dependent processes
involving top quarks.
The Green function formalism is applied to $t\bar t$
production at future $e^+e^-$ colliders with polarized beams.
Lippmann–Schwinger equation is solved numerically for the QCD
chromostatic potential given by the two-loop formula
at large momentum transfers and Richardson ansatz
at intermediate and small ones. The polarization dependent
momentum distributions of top quarks and their decay products
are calculated.
