An up-to-date global QCD analysis of high energy lepton-hadron and hadronhadron interactions is performed to better determine the gluon and quark parton distributions in the nucleon. Improved experimental data on inclusive jet production, in conjunction with precise deep inelastic scattering data, place good constraints on the gluon over a wide range of x; while new data on asymmetries in Drell-Yan processes contribute to better determine the d/u ratio. Comparisons with results of other recent global analyses are made, and the differences are described. Open issues and the general problem of determining the uncertainties of parton distributions are discussed.

TO avoid circumlocutions, we will often use the terminology of the operator product expansion when discussing factorization theorems. In particular, we will use the term "Wilson coefficient" to denote the short-distance coefficient in the standard factorization theorem for deep-inelastic scattering etc.3 102

The impact of recent precision measurements of DIS structure functions and inclusive jet production at the Fermilab Tevatron on the global QCD analysis of parton distribution functions is studied in detail. Particular emphasis is placed on exploring the range of variation of the gluon distribution G(x,Q) allowed by these new data. The strong coupling of G(x,Q) with ␣ s is fully taken into account. A new generation of CTEQ parton distributions, CTEQ4, is presented. It consists of the three standard sets ͓modified minimal subtraction (MS), deep inelastic scattering ͑DIS͒, and leading order ͑LO͔͒, a series that gives a range of parton distributions with corresponding ␣ s 's, and a set with a low starting value of Q. Previously obtained gluon distributions that are consistent with the high E t jet cross section are also discussed in the context of this new global analysis.