This review of unpolarized parton distributions in the perturbative QCD framework examines contemporary issues on next‐to‐leading order studies, assesses the current status of global analysis of these distributions, and discusses the wide scope of physical processes relevant for improving the second‐generation analyses and for resolving the remaining open questions. Subtlies and pitfalls are delineated—with a view of extracting pertinent lessons for the emerging study of polarized parton distributions.