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...