  The kinematic region covered by the LHC experiments probes low values of
Bjorken-$x$. At the scale relevant for $W$ and $Z$ production the central
rapidity region covers $10^{-3} < x < 10^{-1}$. This means that it is the HERA
data which give the most insight into the behaviour of parton distribution
functions (PDFs) for the early phase of running at the LHC. The H1 and ZEUS
experiments are combining their data so as to provide a legacy of HERA results.
The present status of the data combinations and the impact of these data on our
knowledge of parton distribution functions is explored.
