  Precise measurements of the mass and width of the W boson are sensitive to
radiative corrections and can be used to place limits on new physics beyond the
Standard Model and validate the consistency of the model. In particular, the W
boson mass constrains the mass of the, as yet unobserved, Higgs boson and the
width can be used to place limits on the existence of new particles that couple
to the W. Results are presented from proton anti-proton collisions recorded by
the CDF and D0 experiments at the Fermilab Tevatron collider, operating at a
centre of mass energy of 1.96 TeV. The uncertainty on the W mass is determined
to be 76 MeV by CDF and the width, by D0, to be 2011 +/- 90 (stat.) +/- 107
(syst.) MeV.
