This volume constitutes the refereed proceedings of the 26th International Symposium on String Processing and Information Retrieval, SPIRE 2019, held in Segovia, Spain, in October 2019. The 28 full papers and 8 short papers presented in this volume were carefully reviewed and selected from 59 submissions. They cover topics such as: data compression; information retrieval; string algorithms; algorithms; computational biology; indexing and compression; and compressed data structures.