  Reliable knowledge of parton distributions at large x is crucial for many
searches for new physics signals in the next generation of collider
experiments. Although these are generally well determined in the small and
medium x range, it has been shown that their uncertainty grows rapidly for x >
0.1. We examine the status of the gluon and quark distributions in light of new
questions that have been raised in the past two years about large-x parton
distributions, as well as recent measurements which have improved the parton
uncertainties. We perform several specific global fits to answer the
outstanding questions, and to investigate the potential of future experiments,
particularly at HERA, which may provide critical constraints on parton
distributions at large x.
