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We have examined the evidence for the electroweak radiative corrections in the LEP precision data along with the intriguing possibility that the QED corrections only may be sufficient to fit the data. We find that the situation is very sensitive to the precise value of $M_W$. While the world average value of $M_W$ strongly favors nonvanishing electroweak radiative corrections, the QED corrections alone can account for the data within $2\sigma $ in the context of the standard model. We discuss how the precision measurements of $M_W$ can provide a decisive test for the standard model with radiative corrections and give a profound implication for the existence of t-quark and Higgs scalar.

The study of electron-positron collisions at LEP, together with additional measurements from other experiments, in particular those at SLC and at the Tevatron, has allowed for tests of the electroweak Standard Model with unprecedented accuracy. We review the results of the electroweak precision tests and their implications on the determination of the Standard Model parameters, in particular of the Higgs boson mass, and comment on the constraints for possible new physics effects.

The present status of precision electroweak data is reviewed. These data include measurements of e+e- -> f+fbar, taken at the Z resonance at LEP, which are used to determine the mass and width of the Z boson. In addition, measurements have also been made of the forward-backward asymmetries for leptons and heavy quarks, and also the final state polarisation of the tau-lepton. At SLAC, where the electron beam was polarised, measurements were made of the left-right polarised asymmetry, A_LR, and the left-right forward-backward asymmetries for b and c quarks. The mass, MW, and width, GW, of the W boson have been measured at the Tevatron and at LEP, and the mass of the top quark, Mt, has been measured at the Tevatron. These data, plus other electroweak data, are used in global electroweak fits in which various Standard Model parameters are determined. A comparison is made between the results of the direct measurements of MW and Mt with the indirect results coming from electroweak radiative corrections. Using all precision electroweak data fits are also made to determine limits on the mass of the Higgs boson. The influence on these limits of specific measurements, particularly those which are somewhat inconsistent with the Standard Model, is explored. The data are also analysed in terms of the quasi model-independent epsilon variables. Finally, the impact on the electroweak fits of the improvements in the determination of the W-boson and top-quark masses, expected from the Tevatron Run 2, is examined.