The PDF4LHC recommendations for LHC Run II provide updated guidance on the use of parton distribution functions (PDFs) and their uncertainties for LHC physics. The document reviews recent developments in PDF determination, compares the latest PDF sets, and proposes a new method for combining them. It discusses the statistical combination of PDF sets, tools for delivering optimized sets of Hessian eigenvectors or Monte Carlo replicas, and their application to LHC phenomenology. The recommendations emphasize the importance of using a consistent value of the strong coupling constant α_s(m_Z²) and provide guidelines for calculating PDF and PDF+α_s uncertainties. The document also outlines the implications of these recommendations for LHC processes and future directions. The main focus is on the improved combination of PDF sets, which allows for more accurate predictions and reduces uncertainties. The recommendations are based on the latest PDF sets, including CT14, MMHT14, and NNPDF3.0, and provide a framework for their use in LHC analyses. The document concludes with a summary of the key points and future directions for PDF4LHC.The PDF4LHC recommendations for LHC Run II provide updated guidance on the use of parton distribution functions (PDFs) and their uncertainties for LHC physics. The document reviews recent developments in PDF determination, compares the latest PDF sets, and proposes a new method for combining them. It discusses the statistical combination of PDF sets, tools for delivering optimized sets of Hessian eigenvectors or Monte Carlo replicas, and their application to LHC phenomenology. The recommendations emphasize the importance of using a consistent value of the strong coupling constant α_s(m_Z²) and provide guidelines for calculating PDF and PDF+α_s uncertainties. The document also outlines the implications of these recommendations for LHC processes and future directions. The main focus is on the improved combination of PDF sets, which allows for more accurate predictions and reduces uncertainties. The recommendations are based on the latest PDF sets, including CT14, MMHT14, and NNPDF3.0, and provide a framework for their use in LHC analyses. The document concludes with a summary of the key points and future directions for PDF4LHC.