This book constitutes the thoroughly refereed proceedings of the 7th International Workshop on Multi-Agent-Based Simulation, MABS 2006. This was held in Hakodate, Japan, May 8, 2006 as an associated event of AAMAS 2006, the main international conference on autonomous agents and multi-agent systems. The 12 revised full papers presented together with three short papers and two invited papers were carefully reviewed and selected from 25 submissions during two rounds of reviewing.