This book constitutes the refereed proceedings of the 18th International Conference on Network and System Security, NSS 2024, held in Abu Dhabi, United Arab Emirates, during November 20–22, 2024.The 21 full papers presented in this book were carefully reviewed and selected from 62 submissions. They are grouped into these topical sections: authentication and security; privacy and encryption; malware detection and prevention; system security and prevention; network and infrastructure security; blockchain and smart contracts; and data security.