This five-volume set LNCS 15520-15524 constitutes the proceedings of the 31st International Conference on Multimedia Modeling, MMM 2025, held in Nara, Japan, January 8-10, 2025. The 135 full papers and 41 short papers presented in these proceedings were carefully reviewed and selected from 348 submissions. The MMM conference was organized in topics related to multimedia modelling, particularly: audio, image, video processing, coding and compression; multimodal analysis for retrieval applications, and multimedia fusion methods.