A global QCD analysis of the nucleon's parton structure is presented, focusing on the CTEQ5 parton distributions. The analysis incorporates new experimental data from the past two years, including deep inelastic scattering, lepton-pair production asymmetry, W-lepton asymmetry, inclusive jet production, and direct photon production. These data provide constraints on the gluon and quark distributions, particularly the d/u ratio. The analysis compares results with other global studies and discusses open issues in determining parton distribution uncertainties. The paper discusses the impact of new data on parton distribution functions, including the influence of the E866 and CDF experiments on flavor differentiation. It addresses challenges in determining the gluon distribution, particularly from direct photon data, which show discrepancies with conventional QCD calculations. The analysis also explores the role of heavy quarks in perturbative QCD, highlighting the need for accurate treatments of charm quark physics. The CTEQ5 parton distributions are presented in various schemes, including the conventional MS scheme, DIS scheme, and leading order QCD. These distributions are compared with experimental data, showing good agreement with DIS, Drell-Yan, and jet production data. The CTEQ5HJ set is introduced to improve the gluon distribution in the large x region, providing better agreement with jet data. The paper also discusses the importance of accurate parton distribution sets for theoretical and experimental applications, emphasizing the need for consistent and reliable parameterizations. It highlights the challenges in quantifying uncertainties, including experimental and theoretical sources, and the need for further research to refine parton distribution analyses. The analysis concludes that while global QCD analyses continue to improve, there are still open questions that require further investigation to enhance our understanding of parton structure.A global QCD analysis of the nucleon's parton structure is presented, focusing on the CTEQ5 parton distributions. The analysis incorporates new experimental data from the past two years, including deep inelastic scattering, lepton-pair production asymmetry, W-lepton asymmetry, inclusive jet production, and direct photon production. These data provide constraints on the gluon and quark distributions, particularly the d/u ratio. The analysis compares results with other global studies and discusses open issues in determining parton distribution uncertainties. The paper discusses the impact of new data on parton distribution functions, including the influence of the E866 and CDF experiments on flavor differentiation. It addresses challenges in determining the gluon distribution, particularly from direct photon data, which show discrepancies with conventional QCD calculations. The analysis also explores the role of heavy quarks in perturbative QCD, highlighting the need for accurate treatments of charm quark physics. The CTEQ5 parton distributions are presented in various schemes, including the conventional MS scheme, DIS scheme, and leading order QCD. These distributions are compared with experimental data, showing good agreement with DIS, Drell-Yan, and jet production data. The CTEQ5HJ set is introduced to improve the gluon distribution in the large x region, providing better agreement with jet data. The paper also discusses the importance of accurate parton distribution sets for theoretical and experimental applications, emphasizing the need for consistent and reliable parameterizations. It highlights the challenges in quantifying uncertainties, including experimental and theoretical sources, and the need for further research to refine parton distribution analyses. The analysis concludes that while global QCD analyses continue to improve, there are still open questions that require further investigation to enhance our understanding of parton structure.