The two volume set LNCS 15257 + 15258 constitutes the proceedings of the 27th International Conference on Information Security, ISC 2024, held in Arlington, VA, USA, during October 23-25, 2024. The 33 full papers presented in these proceedings were carefully reviewed and selected from 111 submissions. The papers are organized in the following topical sections: Part I - Blockchain; Symmetric-Key Cryptography; Machine Learning; Software Security; Multi-Party Computation; Post-Quantum Cryptography; System Security. Part II - Web Security; Intrusion Detection.