  Electroweak precision observables (EWPO) can give valuable information about
the last unknown paramter of the Standard Model (SM), the Higgs-boson mass
M_H^SM. EWPO can also restrict the parameter space of new physics models (NPM)
such as the Minimal Supersymmetric Standard Model (MSSM). We review the
respective constraints from the W boson mass, the effective leptonic mixing
angle, the anomalous magnetic moment of the muon and electric dipole moments.
Within the MSSM also the lightest Higgs-boson mass, M_h, is discussed as a
precision observable. The EWPO, supplemented with B physics observables and
astrophysical data can be used to determine indirectly the preferred mass
scales of Supersymmetry and M_h.
