LHAPDF is a library implementing a standard to represent Parton Distribution Functions (PDFs) which is ubiquitous in the field of High Energy Physics. PDFs, which describe the structure of the proton, are an essential ingredient for experimental and phenomenological studies at the Large Hadron Collider (LHC). LHAPDF allows PDF fitting collaborations to distribute their results in a format that is interoperable with tools requiring PDFs as input, such as Monte Carlo Event generations. The LHAPDF project maintains a remote repository of PDFs, which can be installed with tools that accompany the library. Please make sure to cite the following paper if you use LHAPDF6 "LHAPDF6: parton density access in the LHC precision era" Eur.Phys.J. C75 (2015) 3, 132 http://arxiv.org/abs/1412.7420