This book constitutes the proceedings of the 31st International Conference on Collaboration Technologies and Social Computing, CollabTech 2025, held in Jakarta, Indonesia, during November 4–7, 2025.The 12 full and 8 short papers presented in this volume were carefully reviewed and selected from 50 submissions. They are grouped into the following topics: Collaborative Learning and Group Interaction; Technology-Mediated Communication and Online Environments; AI in Education: LLMs and Content Generation; Social Interaction, Community and Public Spaces; Systems for Supporting Discourse and Understanding.