This book constitutes the thoroughly refereed postproceedings of the Joint International Workshop on Multi-Agent and Multi-Agent-Based Simulation, MABS 2004, held in New York, NY, USA in July 2004.The 20 revised full papers presented have gone through two rounds of reviewing, selection, and improvement; they present state-of-the-art research results in agent-based simulation and modeling. The papers are organized in topical sections on simulation of multi-agent systems, techniques and technologies, methodology and modeling, social dynamics, and application.