This book constitutes the refereed proceedings of the Third German Conference on Multiagent Systems Technologies, MATES 2005, held in Koblenz, Germany, in September 2005 – co-located with the 28th German Conference on Artificial Intelligence (KI 2005).

The 14 revised full papers presented together with 5 revised short papers and 5 poster papers were carefully reviewed and selected from 54 submissions. The papers are organized in topical sections on workflows and group interaction, reasoning about utility, the dynamics of knowledge, methodology and simulation, agent tools and agent education.