  Future high energy linear electron positron colliders with centre-of-mass
enegies between 90 and 1000 GeV offer a unique opportunity to study precisely
the Standard Model and phenomena from new physics. Most important, the
mechanism of electroweak symmetry breaking can be established in full depth if
one or more Higgs bosons are observed. Precision measurements of electroweak
processes open a window into the multi-TeV energy range for searching for new
physics, which is of particular importance if no light Higgs boson is observed.
