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.