This book constitutes the thoroughly refereed revised selected papers of the 15th International Symposium on Trends in Functional Programming, TFP 2014, held in Soesterberg, The Netherlands, in May 2014. The 8 revised full papers included in this volume were carefully and selected from 22 submissions. TFP is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area.