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. .