This book constitutes the thoroughly refereed postproceedings of the 9th International Workshop on Multi-Agent-based Simulation, MABS 2008, held in Estoril, Portugal, in May 2008.

The 16 revised full papers presented have gone through two rounds of reviewing, selection, and improvement and were selected from 44 submissions; they present state-of-the-art research results in agent-based simulation and modeling. The papers are organized in topical sections on simulation of economic behaviour; modelling and simulation of social behaviou; applications; techniques, infrastructure and technologies as well as methods and methodologies.

IBERAMIA is the international conference series of the Ibero-American Art- cialIntelligencecommunitythathasbeenmeetingeverytwoyearssincethe1988 meeting in Barcelona. The conference is supported by the main Ibero-American societies of AI and provides researchers from Portugal, Spain, and Latin Am- ica the opportunity to meet with AI researchers from all over the world. Since 1998, IBERAMIA has been a widely recognized international conference, with its papers written and presented in English, and its proceedings published by Springer in the LNAI series. This volume contains the papers accepted for presentation at Iberamia 2008, held in Lisbon, Portugal in October 2008. For this conference, 147 papers were submitted for the main track, and 46 papers were accepted. Each submitted paper was reviewed by three members of the Program Committee (PC), coor- nated by an Area Chair. In certain cases, extra reviewerswererecruited to write additional reviews. The list of Area Chairs, PC members, and reviewers can be found on the pages that follow. The authors of the submitted papers represent 14 countries with topics c- ering the whole spectrum of themes in AI: robotics and multiagent systems, knowledge representation and constraints, machine learning and planning, n- ural language processing and AI applications. TheprogramforIberamia2008alsoincludedthreeinvitedspeakers:Christian Lemaitre (LANIA, M exico), R. Michael Young (NCSU, USA) and Miguel Dias (Microsoft LDMC, Lisbon) as well as ?ve workshops.