This two volume constitutes the refereed proceedings of the 18th International Symposium on Foundations and Practice of Security, FPS 2025, held in Brest, France during November 25&27, 2025.The 38 full and 8 short papers presented in this book were carefully reviewed and selected from 91 submissions. The papers were organized in the following topical sections:Part I: Security, Privacy, and Trust in Emerging Distributed Systems; Cyber Resilience and Risk Management in Enterprise Architectures; Formal Methods and Automated Analysis for Secure Software Systems; Machine Learning and Intelligent Systems for Attack Detection and Trust Evaluation; Applications to Industry and Critical Infrastructure. Part II: Advances in Privacy-Preserving Cryptography and Secure Computation; Secure and Intelligent Network Architectures for Next-Generation Communications; Secure, Explainable, and Efficient Machine Learning in Cybersecurity; Short Papers.