The NNPDF3.0 parton distribution functions (PDFs) are determined using a validated methodology that includes a closure test. This set incorporates a wide range of experimental data, including HERA-II deep-inelastic scattering, jet production from ATLAS and CMS, vector boson rapidity and transverse momentum distributions, W+c data, and top quark pair production cross sections. The results are based on LO, NLO, and NNLO QCD theory, along with electroweak corrections. The closure test ensures that the methodological uncertainties are negligible compared to the experimental and theoretical uncertainties. The methodology is validated by generating pseudo-data from a known underlying law and showing that the resulting PDFs accurately reproduce the expected statistical distributions. The NNPDF3.0 PDFs are determined with confidence using a variety of experimental datasets, from HERA-only to a global set including the latest LHC results. The results have phenomenological implications for the upcoming 13 TeV LHC Run, particularly for Higgs production cross-sections. The dataset includes new experimental data such as HERA-II inclusive cross sections, LHC vector boson production data, and W+c production data. The theoretical treatment includes computational tools for perturbative corrections, approximate NNLO treatment of jets, electroweak corrections, and treatment of heavy quark mass effects. The dataset is constructed with kinematic cuts and treatment of correlated systematic uncertainties. The methodology includes a new code with improved algorithms and parametrization. The closure test is performed in three levels, ensuring the robustness of the fitting methodology. The NNPDF3.0 PDFs are provided at LO, NLO, and NNLO in QCD theory, with various values of αs and active flavor numbers. The results are compared with previous PDF sets and show improvements in jet data and strange PDFs. The implications for LHC phenomenology include Higgs production in gluon fusion and new physics particle production at high masses. The results are validated with closure tests and are used for future studies.The NNPDF3.0 parton distribution functions (PDFs) are determined using a validated methodology that includes a closure test. This set incorporates a wide range of experimental data, including HERA-II deep-inelastic scattering, jet production from ATLAS and CMS, vector boson rapidity and transverse momentum distributions, W+c data, and top quark pair production cross sections. The results are based on LO, NLO, and NNLO QCD theory, along with electroweak corrections. The closure test ensures that the methodological uncertainties are negligible compared to the experimental and theoretical uncertainties. The methodology is validated by generating pseudo-data from a known underlying law and showing that the resulting PDFs accurately reproduce the expected statistical distributions. The NNPDF3.0 PDFs are determined with confidence using a variety of experimental datasets, from HERA-only to a global set including the latest LHC results. The results have phenomenological implications for the upcoming 13 TeV LHC Run, particularly for Higgs production cross-sections. The dataset includes new experimental data such as HERA-II inclusive cross sections, LHC vector boson production data, and W+c production data. The theoretical treatment includes computational tools for perturbative corrections, approximate NNLO treatment of jets, electroweak corrections, and treatment of heavy quark mass effects. The dataset is constructed with kinematic cuts and treatment of correlated systematic uncertainties. The methodology includes a new code with improved algorithms and parametrization. The closure test is performed in three levels, ensuring the robustness of the fitting methodology. The NNPDF3.0 PDFs are provided at LO, NLO, and NNLO in QCD theory, with various values of αs and active flavor numbers. The results are compared with previous PDF sets and show improvements in jet data and strange PDFs. The implications for LHC phenomenology include Higgs production in gluon fusion and new physics particle production at high masses. The results are validated with closure tests and are used for future studies.