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 ?rst 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 cro- disciplinary investigation of the applications of trust as a means of increasing security, building con?dence and facilitating collaboration in dynamic open s- tems. The aim of the iTrust conference series is to provide a common forum, bringing together researchers from di?erent academic branches, such as the technology-oriented disciplines, law, social sciences and philosophy, in order to develop a deeper and more fundamental understanding of the issues and ch- 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.