This book constitutes revised selected papers from the 26th International Symposium on Trends in Functional Programming, TFP 2025, held in Oxford, UK, during January 13–16, 2025.The 20 full papers and 2 invited papers presented in this volume were carefully reviewed and selected from 35 submissions. They were categorized under the topical sections as follows: Invited papers; Language Design; Compilation; Semantics; Types; Program Synthesis; Teaching.