This volume constitutes the refereed proceedings of the 24th International Symposium on Intelligent Data Analysis, IDA 2026, held in Leiden, The Netherlands, during April 22–24, 2026.The 33 full papers included in the proceedings were carefully reviewed and selected from 86 submissions. They were organized in topical sections as follows: Foundations of AI/ML; XAI; Representation Learning; Data Mining; and Temporal Data.