  An electron-positron linear collider in the energy range between 500 and 1000
GeV is of crucial importance to precisely test the Standard Model and to
explore the physics beyond it. The physics program is complementary to that of
the Large Hadron Collider. Some of the main physics goals and the expected
accuracies of the anticipated measurements at such a linear collider are
discussed. A short review of the different collider designs presently under
study is given including possible upgrade paths to the multi-TeV region.
Finally a framework is presented within which the realisation of such a project
could be achieved as a global international project.
