This two-volume proceedings set LNCS 15056-15057 constitutes the proceedings of 26th International Conference on Information and Communications Security, ICICS 2024, in Mytilene, Greece, during August 26-28, 2024.The 32 full papers presented in this book were carefully selected and reviewed from 123 submissions. They cover topics related to many aspects of security in information and communication systems, ranging from attacks, to defences, to trust issues, to anomaly-based intrusion detection, to privacy preservation, and to theory and applications of various cryptographic techniques.