Description:This book constitutes the refereed proceedings of the Second German Conference on Multiagent Systems Technologies, MATES 2004, held in Erfurt, Germany, in September 2004.The 22 revised full papers presented together with 2 invited papers were carefully reviewed and selected from 60 submissions. The papers are organized in topical sections on learning and social agents, analysis and security, negotiation and control, agents and software engineering, simulation and agents, and policies and testing.