This book constitutes the refereed proceedings of the 9th International Conference on Frontiers in Cyber Security, FCS 2026, held in Macau, China, during August 3–5, 2026.

The 23 full papers included in this book were carefully reviewed and selected from 79 submissions. They were organized in topical sections as follows:Post-Quantum Lattice Crypto; Secure Data Sharing; Privacy in Distributed Networks; Blockchain & Smart Contract Security;