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.