Top quark studies at future $e^+e^-$ colliders are considered.
Two issues are discussed:
  1. 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.
  2. 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.