The 4-volume set LNCS constitutes the main proceedings of the 25th International Conference on Computational Science, ICCS 2025, which took place in Singapore, Singapore, during July 7&9, 2025.The 64 full papers and 52 short papers presented in these proceedings were carefully reviewed and selected from 162 submissions. The ICCS 2025 main track full papers are organized in volumes 15903 & 15905 (Parts I to III) and the ICCS 2025 main track short papers are included in volume 15906 (Part IV).