  Linear e+e- colliders provide a rich set of opportunities for top quark
physics, crucial for the understanding of electroweak symmetry breaking and for
the search for physics beyond the Standard Model. A ttbar threshold scan in
e+e- annihilation enables a precise measurement in theoretically well-defined
mass schemes with small experimental and theoretical systematic uncertainties.
Above the production threshold, the efficient identification of top pair events
combined with polarized beams provides the potential to extract the form
factors for the top quark couplings with high precision and in a
model-independent way, resulting in excellent sensitivity to physics beyond the
Standard Model. This contribution provides an overview of top physics at linear
colliders based on results from full-simulation studies of top quark pair
production in the detectors proposed for ILC and CLIC. In addition, the
influence of the luminosity spectrum of a 100 km circular e+e- collider (FCCee)
compared to linear colliders on a top threshold scan is briefly discussed.
