  Top quark production in the process $e^+e^- \rightarrow t\bar{t}$ at a future
linear electron positron collider with polarized beams is a powerful tool to
determine the scale of new physics. Studies at the $\ttbar$ threshold will
allow for precise determination of the top quark mass in a well defined
theoretical framework. At higher energies vector, axial vector and tensorial CP
conserving couplings can be separately determined for the photon and the $Z^0$
component in the electro-weak production process. The sensitivity to new
physics would be dramatically improved w.r.t. to what expected from LHC for
electroweak couplings.
