The three-volumes LNCS 15648, 15649, 15650 set constitutes the refereed proceedings of the 25th International Conference on Computational Science and Its Applications - ICCSA 2025, held in Istanbul, Turkey, during June 30&July 3, 2025.  The 71 full papers, 6 short papers, and 1 PHD showcase paper were carefully reviewed and selected from 269 submissions. The papers have been organized in topical sections as follows: Part I: Computational Methods, Algorithms and Scientific Applications; High Performance Computing and Networks; Geometric Modeling, Graphics and Visualization; Advanced and Emerging Applications; Information Systems and Technologies; Urban and Regional Planning. Part II: Information Systems and Technologies;  Part III: Information Systems and Technologies; Urban and Regional Planning; PHD Showcase Paper; Short papers.