This book constitutes the revised selected papers of the 13th International Symposium on Foundations and Practice of Security, FPS 2020, held in Montréal, QC, Canada, in December 2020.

The 11 full papers and 1 short paper presented in this book were carefully reviewed and selected from 23 submissions. They cover a range of topics such as Analysis and Detection; Prevention and Efficiency; and Privacy by Design.