I discuss recent developments in the determination of parton distributions
from global fits. I concentrate on the errors associated with these parton
distributions and with the physical quantities which are determined in terms of
them. I outline the various techniques used to quantify the uncertainties due
to errors on experimental data used in the fits, and provide a number of
examples of predictions with their uncertainties. However, I demonstrate that
this source of errors may, in some circumstances, be less important than errors
due to underlying assumptions in the fitting procedure and due to the
incomplete nature of the theoretical framework currently employed.Comment: Invited talk at the 14th Topical Conference on Hadron Collider
Physics (HCP2002), Sept 30th - Oct 4th 2002, Karlsruhe, Germany. 13 pages, 11
figures, uses svmult.cls and physmubb.st
