Physics with e+e− linear colliders

The physics potential of e+e− linear colliders is briefly summarized for center-of-mass energies up to 500 GeV in the first phase, and up to 2 TeV in the second phase. The machines will enable us to perform precision studies of the top quark and the electroweak gauge bosons in the Standard Model. They are ideal instruments to search for Higgs particles and to investigate their characteristic properties. In the area beyond the Standard Model, new particles and interactions can be explored. The accelerators provide unique opportunities, in particular, for investigating supersymmetric particles and the structure of the underlying unified theory. The programme of e+e− linear colliders is largely complementary to the programme of the pp collider LHC. By operating both types of machines, the physics up to the TeV energy range can be explored in a conclusive way.