n e Grid2003 Project has deployed a multi-virfual organization, application-driven grid laboratory ('"Grid3'7 that has sustained for several months the production-level services required by physics experiments of the Large Hadron Collider at CERN (ATLAS and CMS), the Sloan Digital Sky Survey project, the gravitational wave search experiment LIGO, the BTeV mperiment at Fermilab, as well as applications in molecular structure analysis and genome analysis, and computer science research projects in such areas as job and data scheduling. The deployed infiastmcture has been operating since Noisniber 2003 with 27 sites, apeak of 2800 processors, work loads fiom 10 different applications exceeding 1300 simultaneous jobs, and data transfers among sites of greater than 2 TBiday. We describe the principles that have guided the development of this unique infrastructure and the practical experiences that have resultedfiom its creation and use. We discuss application requirements for grid services deployment and con$guration. monitoring infiastnic fure, application performance, metrics. and operational experiences. We also summarize lessons learned.