  We review the empirical evidence for the validity of the Standard Electroweak
Theory in Nature. The experimental data are interpreted in terms of an
effective Lagrangian for Z physics, allowing for potential sources of SU(2)
violation and containing the predictions of the Standard Electroweak Theory as
a special case. Particular emphasis is put on discriminating loop corrections
due to fermion-loop vector-boson propagator corrections on the one hand, from
corrections depending on the non-Abelian structure and the Higgs sector on the
other hand. Results from recently obtained fits of the Higgs-boson mass are
reported, yielding M_H < 430 GeV [680 GeV] at 95% C.L. based on the input of
\swbar^2(\LEP+\SLD)_{`97} = 0.23152 +- 0.00023 [\swbar^2(\LEP)_{`97} = 0.23196
+- 0.00028]. The LEP2 data provide first direct experimental evidence for
non-zero non-Abelian couplings among the electroweak vector bosons.
