The papers contained in this volume were presented at the 11th Conference on String Processing and Information Retrieval (SPIRE), held Oct. 5-8, 2004 at the Department of Information Engineering of the University of Padova, Italy. They wereselected from 123 paperssubmitted in responseto the call for papers. In addition, there were invited lectures by C.J. van Rijsbergen (University of Glasgow, UK) and Setsuo Arikawa (Kyushu University, Japan). In view of the large number of good-quality submissions, some were accepted this year also as short abstracts. These also appear in the proceedings. Papers solicited for SPIRE 2004 were meant to constitute original contri- tions to areas such as string pattern searching, matching and discovery; data compression; text and data mining; machine learning; tasks, methods, al- rithms, media, and evaluation in information retrieval; digital libraries; and - plications to and interactions with domains such as genome analysis,speech and naturallanguageprocessing,Web links and communities, and multilingual data. SPIRE has its origins in the South American Workshop on String Proce- ing which was ?rst held in 1993. Starting in 1998, the focus of the symposium was broadened to include the area of information retrieval due to the common emphasisoninformationprocessing.The?rst10meetingswereheldinBeloH- izonte (Brazil, 1993), Valparaiso (Chile, 1995), Recife (Brazil, 1996), Valparaiso (Chile, 1997), Santa Cruz (Bolivia, 1998), Cancun (Mexico, 1999), A Coruna " (Spain, 2000), Laguna San Rafael (Chile, 2001), Lisbon (Portugal, 2002), and Manaus (Brazil, 2003).