This book constitutes the proceedings of the 23rd European Conference on Multi-Agent Systems, EUMAS 2026, held in Malmo, Sweden, during September 21-25, 2026.

The 37 full papers and 5 demonstrators included in this volume were carefully reviewed from 86 submissions. The papers cover the following topical sections: Learning in Multi-Agent Systems; Coordination, Organizations, Institutions, Norms and Ethics; Engineering Multi-Agent Systems; Knowledge Representation, Reasoning and Verification for MAS; MAS for Robotic Systems and Control; Multi-Agent Based Simulation; Human-Centric MAS; Explainable MAS; and Demonstrators.