Top quark studies at future $e^+e^-$ colliders are considered.
Two issues are discussed:
- Some results are presented on the decays of top quarks. Energy
distributions of charged leptons and neutrinos in $t\to bW\to be^+\nu$
and jets in $t\to bW\to b\bar du$ decays are sensitive to the
structure of $tbW$ vertex. Distributions of charged leptons from top
decays are particularly useful in polarization studies whereas
neutrinos are sensitive to deviations from the Standard Model.
- Recent calculations are reviewed on the top quark pair production
in $e^+e^-$ annihilation. The differential cross sections in the
threshold region can lead to an accurate determination of the top
quark mass and the interquark potential. The effects of the top-Higgs
Yukawa coupling and some higher order QCD corrections are also under
control.