Invited papers -- r-indexing the eBWT -- Unicode at Gigabytes per Second -- Combinatorics -- Longest Common Rollercoasters -- Minimal unique palindromic substrings after single-character substitution -- Permutation-constrained Common String Partitions with Applications -- All instantiations of the greedy algorithm for the shortest superstring problem are equivalent -- String Covers of a Tree -- Compression -- Grammar Index By Induced Suffix Sorting -- An LMS-based Grammar Self-index with Local Consistency Properties -- On the approximation ratio of LZ-End to LZ77 -- Data Structures -- Computing the original eBWT faster, simpler, and with less memory -- Extracting the Sparse Longest Common Pre x Array from the Suffix Binary Search Tree -- findere: fast and precise approximate membership query -- Repeats -- Improved Topic Modeling in Twitter through Community Pooling -- Lower Bounds for the Number of Repetitions in 2D Strings -- On Stricter Reachable Repetitiveness Measures -- Information Retrieval -- Improved Topic modeling in Twitter through Community Pooling -- TSXor: A Simple Time Series Compression Algorithm -- Pattern Matching -- Exploiting Pseudo-Locality of Interchange Distance -- Position Heaps for Cartesian-tree Matching on Strings and Tries.

This book constitutes the refereed proceedings of the 27th International Symposium on String Processing and Information Retrieval, SPIRE 2021, held in Lille, France, in October 2021.* The 14 full papers and 4 short papers presented together with 2 invited papers in this volume were carefully reviewed and selected from 30 submissions. They cover topics such as: data structures; algorithms; information retrieval; compression; combinatorics on words; and computational biology. *The symposium was held virtually.