This book constitutes the proceedings of the 26th International Working Conference on Requirements Engineering - Foundation for Software Quality, REFSQ 2020, which was due to be held in Pisa, Italy, in March 2020. Due to the COVID-19 pandemic the conference was held virtually in June 2020. The 14 full papers and 7 short papers in this volume were carefully reviewed and selected from 84 submissions. The papers are organized in the following topical sections: requirements specification; requirements documentation; privacy and legal requirements; stakeholders feedback and training; agile methods and requirements comprehension; requirements modelling; requirements visualization.