  Experiments in the energy range from the scale of electroweak symmetry
breaking to the TeV scale are expected to be crucial for unraveling the
microscopic structure of matter and forces. The high precision which should be
achieved in experiments at lepton colliders, is a necessary ingredient for
providing a comprehensive picture of the mechanism breaking the electroweak
symmetries and generating mass, the unification of forces, involving most
likely supersymmetry, and the structure of space-time at small distances. In
addition, clarifying the nature of the particles which build up cold dark
matter in the universe, needs a lepton collider to match the high experimental
precision which will be reached in cosmology experiments.
