This book constitutes the refereed proceedings of the 16th International Symposium on Foundations and Practice of Security, FPS 2023, held in Bordeaux, France, during December 11–13, 2023. The 27 regular and 8 short papers presented in this book were carefully reviewed and selected from 80 submissions. The papers have been organized in the following topical sections:Part I: AI and cybersecurity, security analysis, phishing and social network, vulnerabilities and exploits, network and system threat, malware analysis. Part II : security design, short papers.