  Effective theories provide a powerful tool for testing the Standard Model and
for searching for the effects of new physics in a model-independent manner. In
general one assumes that the effects of new physics characterized by a
high-energy scale may be observed at low-energies only through quantum
corrections. These quantum corrections may be described by effective operators
which are constructed from the fields of the low-energy theory; the
coefficients of these operators may be measured via experiment, but a
theoretical determination is only possible once the complete theory is known.
Because the existence or non-existence of a light physical Higgs boson has not
yet been established the inclusion or exclusion of the Higgs field in the
construction of the effective Lagrangian is open to debate. For this reason we
discuss both the linearly realized effective Lagrangian, which includes a light
physical Higgs boson, and the chiral Lagrangian, where the Higgs boson has been
removed by a formal integration. In each scenario the contributions to oblique
parameters and to W-pair-production amplitudes are discussed. Where possible
relationships between the two effective Lagrangians are given.
