The papers contained in this volume were presented at the 12th edition of the International Symposium on String Processing and Information Retrieval (SPIRE), held November 2-4, 2005, in Buenos Aires, Argentina. They were - lected from 102 papers submitted from 25 countries in response to the Call for Papers.Atotalof27submissionswereacceptedasfullpapers,yieldinganacc- tancerateofabout26%.Inviewofthelargenumberofgood-qualitysubmissions the conference program also included 17 short papers that also appear in the proceedings.In addition, the Steering Committee invited the following speakers: Prabhakar Raghavan (Yahoo! Research, USA), Paolo Ferragina (University of Pisa, Italy), and Gonzalo Navarro (University of Chile, Chile). Papers solicited for SPIRE 2005 were meant to constitute original cont- butions to areas such as string processing (dictionary algorithms, text sear- ing, pattern matching, text compression, text mining, natural language p- cessing, and automata-basedstring processing); information retrieval languages, applications, and evaluation (IR modeling, indexing, ranking and ?ltering, - terface design, visualization, cross-lingual IR systems, multimedia IR, digital libraries,collaborativeretrieval,Web-relatedapplications,XML, information- trievalfromsemi-structureddata,textmining,andgenerationofstructureddata from text); and interaction of biology and computation (sequencing and app- cations in molecular biology, evolution and phylogenetics, recognition of genes and regulatory elements, and sequence-driven protein structure prediction).