This book is the result of the workshop "Deception, Fraud, and Trust in Agent Societies", held in Barcelona on June 4, 2000 as part of the Autonomous Agents 2000 Conference, and organized by Rino Falcone, Munindar Singh, and Yao-Hua Tan. The aim of the workshop was to bring together researchers from di?- ent ?elds (Arti?cial Intelligence, Multi-Agent Systems, Cognitive Science, Game Theory, and Social and Organizational Sciences) that could contribute to a b- ter understanding of trust and deception in agent societies. The workshop scope included theoretical results as well as their applications in human-computer - teraction and electronic commerce. This book includes the revised and extended versions of the works presented at the workshop, incorporating many points that emerged in our discussions, as well as invited papers from experts in the ?eld, which in our view allows a complete coverage of all relevant issues. We gratefully acknowledge the ?nancial support from the Italian National Research Council - Institute for Cognitive S- ence and Technology and the ALFEBIITE European Project, contract number IST-1999-10298. We would like to express our gratitude to Cristiano Castelfranchi for his stimulating and valuable comments and suggestions both for the organization of the workshop and for the preparation of this book.