  We present a new set of parton distributions obtained at NNLO. These differ
from the previous sets available at NNLO due to improvements in the theoretical
treatment. In particular we include a full treatment of heavy flavours in the
region near the quark mass. In this way, an essentially complete set of NNLO
partons is presented for the first time. The improved treatment leads to a
significant change in the gluon and heavy quark distributions, and a larger
value of the QCD coupling at NNLO, alpha_S(M_Z^2) = 0.1191 +/- 0.002(expt.) +/-
0.003(theory). Indirectly this also leads to a change in the light partons at
small x and modifications of our predictions for W and Z production at the LHC.
As well as the best-fit set of partons, we also provide 30 additional sets
representing the uncertainties of the partons obtained using the Hessian
approach.
