The precise determination of parton distribution functions (PDFs) is of
fundamental importance for the physics at the LHC.
For example, precision measurements of electroweak observables, as
the W-boson mass and the weak-mixing angle, the Higgs cross-section
predictions, as well as various searches for physics beyond the standard
model, are currently limited by the incomplete knowledge of the PDFs.
The LHC experiments have performed several measurements of jets,
Drell-Yan, prompt-photon, and top-antitop processes providing
additional constraints to the PDFs which are complementary to those of
deep-inelastic scattering (DIS) data. The inclusion of the LHC
measurements into the global parton density fits allows the reduction
of the PDF uncertainties.