This proceedings contains the papers presented at PPoPP'03, the ACM Symposium on Principles and Practice of Parallel Programming 2003, held in San Diego, California as part of the Federated Computing Research Conference (FCRC'03).The program committee selected 20 papers for presentation at the conference out of 45 papers submitted for review. All of the papers received at least three reviews, with the vast majority receiving four or more. There were good papers that we were unable to accept for presentation because of the conference format.Each paper was judged with respect to its originality, technical contribution, and presentation. The final published version of each paper may differ, in some cases substantially, from the initial submission. The conference selection process does not constitute a complete review of the work. It is expected that many of the papers published in PPoPP'03 will be further revised and published in archival journals.