PDF constraints at ths LHC

At the hadrons colliders, the parton density functions (PDF) play a major role in the determination of the theoretical cross-sections of all physic processes. At the LHC, the statistical fluctuations are expected to be negligible for many processes, and the PDFs will be the major source of the systematic uncertainty. The aim of this talk is to present how the LHC data could help to constrain the modelling and the uncertainties on PDFs. The talk reviews the expectations from both ATLAS and CMS collaborations, and also raises the potential theoretical and experimental issues.