  The accurate determination of the Parton Distribution Functions (PDFs) of the
proton is an essential ingredient of the Large Hadron Collider (LHC) program.
PDF uncertainties impact a wide range of processes, from Higgs boson
characterisation and precision Standard Model measurements to New Physics
searches. A major recent development in modern PDF analyses has been to exploit
the wealth of new information contained in precision measurements from the LHC
Run I, as well as progress in tools and methods to include these data in PDF
fits. In this report we summarise the information that PDF-sensitive
measurements at the LHC have provided so far, and review the prospects for
further constraining PDFs with data from the recently started Run II. This
document aims to provide useful input to the LHC collaborations to prioritise
their PDF-sensitive measurements at Run II, as well as a comprehensive
reference for the PDF-fitting collaborations.
