ELECTROWEAK THEORY AND THE 1996 97 PRECISION ELECTROWEAK DATA/

We review the empirical evidence for the validity of the Standard Elec troweak Theory in Nature. The experimental data are interpreted in ter ms of an effective Lagrangian for Z physics, allowing for potential so urces of SU(2) violation and containing the predictions of the Standar d Electroweak Theory as a special case. Particular emphasis is put on discriminating loop corrections due to fermion-loop vector-boson propa gator corrections on the one hand, from corrections depending on the n on-Abelian structure and the Higgs sector on the other hand. Results f rom recently obtained fits of the Higgs-boson mass are reported, yield ing M-H less than or similar to 430 GeV [680 GeV] at 95% C.L. based on the input of (s) over bar(w)(2)(LEP + SLD)('97) = 0.23152 +/- 0.00023 [(s) over bar(w)(2)(LEP)('97) = 0.23196 +/- 0.00028]. The LEP2 data p rovide first direct experimental evidence for Iron-zero non-Abelian co uplings among the electroweak vector bosons.