  Studying the properties of the W boson plays a key role in precision tests of
the Standard Model. The key measurements performed over the last decade will be
reviewed. W-pair and single-W cross-sections and W decay branching fractions
are determined and agree well with theoretical predictions. Including the
analysis of differential distributions, trilinear and quartic couplings of the
W boson to the other gauge bosons are extracted. A precise measurement of the
mass and width of the W boson is presented. The W mass is in good agreement
with the one obtained indirectly from an analysis of other electroweak data
measured at LEP and SLD. Some of the results presented in this article are
preliminary.
