This volume constitutes the proceedings of 31st International Conference on Cooperative Information Systems, CoopIS 2025, held in Marbella, Spain, during October 20-22, 2025. The 24 full papers and 21 short papers included in this book were carefully reviewed and selected from 128 submissions. They were organized in topical sections as follows: Invited Speakers; Data-Driven and Predictive Process Analytics; Neuro-Symbolic Systems and Knowledge Graphs; Process Conformance, Integrity and Compliance; Intelligent and Secure Connected Systems; Process Discovery and Variability; Architecture Engineering and Governance of Information Systems; and Short Papers.