This volume constitutes the proceedings of the 4th International Conference on Trust Management, held in Pisa, Italy during 16-19 May 2006. The conference followed successful International Conferences in Crete in 2003, Oxford in 2004 and Paris in 2005. The first three conferences were organized by iTrust, which was a working group funded as a thematic network by the Future and Emerging Technologies (FET) unit of the Information Society Technologies (IST) program of the European Union. The purpose of the iTrust working group was to provide a forum for cross- disciplinary investigation of the applications of trust as a means of increasing security, building confidence and facilitating collaboration in dynamic open sys- tems. The aim of the iTrust conference series is to provide a common forum, bringing together researchers from diff erent academic branches, such as the technology-oriented disciplines, law, s ocial sciences and philosophy, in order to develop a deeper and more fundamental understanding of the issues and chal- lenges in the area of trust management in dynamic open systems. The response to this conference was excellent; from the 88 papers submitted to the conference, we selected 30 full papers for presentation. The program also included one keynote address, given by Cristiano Castelfranchi; an industrial panel; 7 technology demonstrations; and a full day of tutorials. The running of an international conference requires an immense effort from all parties involved. We would like to thank the people who served on the Program Committee and the Organizing Committee for their hard work. In particular, we would like to thank the people at the Institute for Informatics and Telematics at the Italian National Research Council (IIT-CNR) for handling the logistics for the conference. We wish to thank also the IIT-CNR, University of Trento and ERCIM STM WG for the financial support for iTrust 200