Thisvolumecontainsthe66contributedpapersandabstractsofthethreeinvited lecturespresentedatthe11thAnnualEuropeanSymposiumonAlgorithms(ESA 2003), held in Budapest, September 16-19, 2003. The papers in each section of the proceedings are arranged alphabetically. The three distinguished invited speakers were Bernard Chazelle, Roberto Tamassia, and Eva Tardos. Forthesecondtime, ESAhadtwotracks, withseparateprogramcommittees, which dealt respectively with: The design and mathematical analysis of algorithms (the "Design and Analysis" track); Real-world applications, engineering, and experimental...