Abstract
I discuss the current state of knowledge of PDFs, concentrating on the MSTW
set. I particularly emphasize the sources of uncertainty, experimental,
procedural and theoretical, and show how these can lead to differences between
different PDF sets. The predictions for processes measured at the LHC and the
possible tests these can provide on PDFs are illustrated. The predictions
for the Higgs cross section at both the Tevatron and the LHC are summarised
and the correlation with other LHC processes introduced.