  The problems of the origin of mass and of electro-weak symmetry breaking are
central to the programme of research in particle physics, at present and in the
coming decades. This paper reviews the potential of high energy, high
luminosity e+e- linear colliders in exploring the Higgs sector,to extend and
complement the data which will become available from hadron colliders. The
accuracy of measurements of the Higgs boson properties will not only probe the
validity of the Higgs mechanism but also provide sensitivity to New Physics
beyond the Standard Model.
