An overview is presented of the characteristics of HEP computing and its mapping to the Grid paradigm. This is followed by a synopsis of the main experiences and lessons learned by HEP experiments in their use of DataGrid middleware using both the EDG application testbed and the LCG production service. Particular reference is made to experiment

data challenges

, and a forward look is given to necessary developments in the framework of the EGEE project.
Keywords applications - EDG - EGEE - Grid - HEP - LCG - LHC - middleware