Description:This book constitutes the refereed proceedings of the 12th International Conference on String Processing and Information Retrieval, SPIRE 2005, held in Buenos Aires, Argentina in November 2005.The 27 revised full papers and 17 revised short papers presented were carefully reviewed and selected from 102 submissions. The papers address current issues in all aspects of string processing, information retrieval, pattern matching, computational biology, semi-structured data, and related applications.