PDF4LHC recommendations for Run II

The interpretation of LHC measurements requires a careful estimate of various sources of uncertainties that affect theoretical calculations. In this contribution, we present the PDF4LHC Working Group recommendations for the usage of sets of parton distribution functions (PDFs) at the LHC Run II. We review the construction and validation of the PDF4LHC15 combined sets, and study some of their phenomenological implications. We also address some recent criticism of these recommendations.